TortoiseGitProc and TGitCache crash on repositories with broken core.worktree path
**What steps will reproduce the problem?**
1. Have a repository with (a submodule and) `.git` file pointing to the superproject
2. Rename the folder in explorer
3. Refresh the view or open TortoiseGitProc
**What is the expected output? What do you see instead?**
TGitCache crashes, but restarts immediately.
**What version of TortoiseGit and Git are you using? On what operating system?**
TortoiseGit 2.9.0.0
issue