LogDlg: Access violation in gitdll when multi-pack-index exists

I did tortoise git log on a large repository with large packfiles. When clicking on one log entry to see the full info, Tortoise crashes with an access violation.

I checked out the TortoiseGit master, built and ran it to pinpoint the exception:

Since this is the second mysterious error in packfile.c in a couple of weeks, I still suspect that there may be concurrency issues.