### Please describe the problem.

I'm unable to use adjusted branches (`---unlock`) on WSL because of sqlite crashes. `smudge` tends to fail with output like:

```
sqlite worker thread crashed: user error (SQLite3 returned ErrorProtocol while attempting to perform prepare "SELECT null from content limit 1": locking protocol(while opening database connection))
git-annex: sqlite query crashed
CallStack (from HasCallStack):
  error, called at ./Database/Handle.hs:98:42 in main:Database.Handle
git-annex: smudge: 1 failed
error: external filter 'git-annex smudge --clean -- %f' failed 1
error: external filter 'git-annex smudge --clean -- %f' failed
```

### What steps will reproduce the problem?

```
git init test
cd test
git annex init test
git annex upgrade
echo asdf > asdf
git annex add asdf # fails for some reason on DrvFs
git annex add asdf # works when executed second time
git annex sync
git annex --debug adjust --unlock
```


### What version of git-annex are you using? On what operating system?

Windows 10 Pro v1903 build 18362.207 - WSL (Arch)

```
git-annex version: 7.20190615-g0bd9e8c0e2
build flags: Assistant Webapp Pairing S3 WebDAV Inotify DBus DesktopNotify TorrentParser MagicMime Feeds Testsuite
dependency versions: aws-0.21.1 bloomfilter-2.0.1.0 cryptonite-0.26 DAV-1.3.3 feed-1.1.0.0 ghc-8.6.5 http-client-0.6.4 persistent-sqlite-2.9.3 torrent-10000.1.1 uuid-1.3.13 yesod-1.6.0
key/value backends: SHA256E SHA256 SHA512E SHA512 SHA224E SHA224 SHA384E SHA384 SHA3_256E SHA3_256 SHA3_512E SHA3_512 SHA3_224E SHA3_224 SHA3_384E SHA3_384 SKEIN256E SKEIN256 SKEIN512E SKEIN512 BLAKE2B256E BLAKE2B256 BLAKE2B512E BLAKE2B512 BLAKE2B160E BLAKE2B160 BLAKE2B224E BLAKE2B224 BLAKE2B384E BLAKE2B384 BLAKE2S256E BLAKE2S256 BLAKE2S160E BLAKE2S160 BLAKE2S224E BLAKE2S224 BLAKE2SP256E BLAKE2SP256 BLAKE2SP224E BLAKE2SP224 SHA1E SHA1 MD5E MD5 WORM URL
remote types: git gcrypt p2p S3 bup directory rsync web bittorrent webdav adb tahoe glacier ddar hook external
operating system: linux x86_64
supported repository versions: 5 7
upgrade supported from repository versions: 0 1 2 3 4 5 6
local repository version: 7
```


### Terminal log

[[!format sh """
$ git init test
Initialized empty Git repository in /mnt/d/debug/test/.git/
$ cd test
$ git annex init test
init test
  Detected a filesystem without fifo support.

  Disabling ssh connection caching.
ok
(recording state in git...)
$ git annex upgrade
upgrade (v5 to v6...) (v6 to v7...) ok
$ echo asdf > asdf
$ git annex add asdf
add asdf
git-annex: .git/annex/othertmp/asdf.0/asdf: rename: permission denied (Permission denied)
failed
git-annex: add: 1 failed
zsh: exit 1     git annex add asdf
$ git annex add asdf
add asdf ok
(recording state in git...)
$ git annex sync
commit
[master (root-commit) 54e120b] git-annex in test
 1 file changed, 1 insertion(+)
 create mode 120000 asdf
ok
$ git annex --debug adjust --unlock
[2019-07-06 11:23:39.4031313] read: git ["--version"]
[2019-07-06 11:23:39.4128108] process done ExitSuccess
adjust [2019-07-06 11:23:39.4137008] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","symbolic-ref","-q","HEAD"]
[2019-07-06 11:23:39.4273287] process done ExitSuccess
[2019-07-06 11:23:39.4276698] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","show-ref","refs/heads/master"]
[2019-07-06 11:23:39.4436791] process done ExitSuccess
[2019-07-06 11:23:39.4440342] call: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","show-ref","--verify","-q","refs/heads/adjusted/master(unlocked)"]
[2019-07-06 11:23:39.4571275] process done ExitFailure 1
[2019-07-06 11:23:39.4579141] call: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","update-ref","refs/basis/adjusted/master(unlocked)","refs/heads/master"]
[2019-07-06 11:23:39.4740989] process done ExitSuccess
[2019-07-06 11:23:39.4745965] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","mktree","--batch","-z"]
[2019-07-06 11:23:39.4770107] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","ls-tree","--full-tree","-z","-r","-t","--","refs/basis/adjusted/master(unlocked)"]
[2019-07-06 11:23:39.4940556] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","cat-file","--batch"]
[2019-07-06 11:23:39.4960848] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","cat-file","--batch-check=%(objectname) %(objecttype) %(objectsize)"]
[2019-07-06 11:23:39.5412121] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","-c","diff.external=","-c","filter.annex.smudge=","-c","filter.annex.clean=","diff","--cached","--raw","-z","--abbrev=40","-G^/annex/objects/","--diff-filter=AMUT","--no-renames","--ignore-submodules=all","--no-ext-diff"]
[2019-07-06 11:23:39.5743181] process done ExitSuccess
[2019-07-06 11:23:39.5754474] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","hash-object","-w","--stdin-paths","--no-filters"]
[2019-07-06 11:23:39.5981937] process done ExitSuccess
[2019-07-06 11:23:39.5990927] process done ExitSuccess
[2019-07-06 11:23:39.6010222] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","commit-tree","69b3149d64ac2eb225c6f5336fa15c518dcd4d83","--no-gpg-sign","-p","refs/basis/adjusted/master(unlocked)"]
[2019-07-06 11:23:39.6194551] process done ExitSuccess
[2019-07-06 11:23:39.6199068] call: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","update-ref","-m","entering adjusted branch","refs/heads/adjusted/master(unlocked)","c4e772ae22f9b1146b798404d85268ea3ca40e03"]
[2019-07-06 11:23:39.6402592] process done ExitSuccess

[2019-07-06 11:23:39.6409432] call: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","checkout","adjusted/master(unlocked)","--progress"]
sqlite worker thread crashed: user error (SQLite3 returned ErrorProtocol while attempting to perform prepare "SELECT null from content limit 1": locking protocol(while opening database connection))
git-annex: thread blocked indefinitely in an MVar operation
error: external filter 'git-annex smudge -- %f' failed 1
error: external filter 'git-annex smudge -- %f' failed
Switched to branch 'adjusted/master(unlocked)'
sqlite worker thread crashed: user error (SQLite3 returned ErrorProtocol while attempting to perform prepare "SELECT null from content limit 1": locking protocol(while opening database connection))
git-annex: sqlite query crashed
CallStack (from HasCallStack):
  error, called at ./Database/Handle.hs:98:42 in main:Database.Handle
git-annex: smudge: 1 failed
error: external filter 'git-annex smudge --clean -- %f' failed 1
error: external filter 'git-annex smudge --clean -- %f' failed
[2019-07-06 11:24:03.3626765] process done ExitSuccess
ok
[2019-07-06 11:24:03.372672] process done ExitSuccess
[2019-07-06 11:24:03.3742067] process done ExitSuccess
[2019-07-06 11:24:03.3756292] process done ExitSuccess
"""]]

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)
Yes, on macOS & HFS+ :)

