fix handling of corrupted data received from git remote

Recover from corrupted content being received from a git remote due eg to a
wire error, by deleting the temporary file when it fails to verify. This
prevents a retry from failing again.

Reversion introduced in version 8.20210903, when incremental verification
was added.

Only the git remote seems to be affected, although it is certianly
possible that other remotes could later have the same issue. This only
affects things passed to getViaTmp that return (False, UnVerified) due to
verification failing. As far as getViaTmp can tell, that could just as well
mean that the transfer failed in a way that would resume, so it cannot
delete the temp file itself. Remote.Git and P2P.Annex use getViaTmp internally,
while other remotes do not, which is why only it seems affected.

A better fix perhaps would be to improve the types of the callback
passed to getViaTmp, so that some other value could be used to indicate
the state where the transfer succeeded but verification failed.

Sponsored-by: Boyd Stephen Smith Jr.

doc/bugs/Failure_to_get_small_files_over_P2P_protocol.mdwn

@@ -115,3 +115,6 @@ Both servers are debian.
 I've been using git annex for years now, some periods more intensively than others. The only data I've lost I can only blame on my own stupidity, even after a terminal disk failure I managed to recover almost everything with a reinject. I'm still using it entirely cli though, no assistants or gui for me.
 
 [[!meta title="corrupted tmp file can prevent getting an object"]]
+
+> [[fixed|done]] (the related issue that I discovered in comment #1
+> specifically) --[[Joey]]