### Please describe the problem.
git annex checkpresentkey does not refuse to run in bare repos, as many commands do, but seems to report all keys as absent.


### What steps will reproduce the problem?
This is a simple example starting from nothing, but in every bare repo I test, regardless if I use batch or not, all keys are reported absent. Observe that the key can be cat'd directly out of the git annex directory in both bare and non-bare, was moved to the bare via git annex sync, yet shows 1 for present in the non-bare and 0 for the bare:

[[!format sh """
mkdir repro
cd repro
mkdir bare nonbare
cd bare
git init --bare
cd ../nonbare
git clone ../bare .
git annex init
echo hello > greeting
git annex add greeting
git commit -m update
git annex sync --content
git annex sync --content
echo SHA256E-s6--5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03 | git annex checkpresentkey --batch
cat .git/annex/objects/*/*/SHA256E-s6--5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03/SHA256E-s6--5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03
cd ../bare
echo SHA256E-s6--5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03 | git annex checkpresentkey --batch
cat annex/objects/*/*/SHA256E-s6--5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03/SHA256E-s6--5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03
"""]]



### What version of git-annex are you using? On what operating system?
Debian Testing, git annex version 8.20200330-1


### Please provide any additional information below.

[[!format sh """
# If you can, paste a complete transcript of the problem occurring here.
# If the problem is with the git-annex assistant, paste in .git/annex/daemon.log


# End of transcript or log.
"""]]

### 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)

Oh it's great, especially the low level plumbing commands. I use it for all my backups by first backup up each machine into a Bup repo, and then storing the bup packs/indices in git-annex, which I use for sync'ing across machines.