fix a place where the inode cache could potentially have gotten stale

fix a place where the inode cache could potentially have gotten stale

When git-annex lock repopulates the object file by copying an associated
file that still has its content, it negected to update the inode cache.

I was not able to actually get this code to successfully repopulate the
object file; the associated file gets replaced with a dangling pointer
before unlock is able to do that. (By what I'm not sure..
reconcileStaged?) Which might be itself a bug, but
anyway this makes me doubtful that this was really leading to a stale
inode cache. Still, in case there is some situation in which it does
work, fixed it to update the inode cache.