tg update sometimes doesn't stop if git fails

[greenrd]

e.g. due to an editor/IDE holding the index lock, we may see:

fatal: Unable to create '/home/robin/git/backend/.git/index.lock': File exists.

If no other git process is currently running, this probably means a
git process crashed in this repository earlier. Make sure no other git
process is running and remove the file manually to continue.

but then tg update continuing.

In this case it was tg update -a, but I'm not sure that's relevant.