theia: [git][diff][question] Dirty diff manager throws an error

when either right or left is not under version control.

It does not cause a problem, but can we handle it on the frontend? So do not execute git show when something is not under version control.

Alternatively, git backend can handle this and return either undefined or something else.

I have assigned to you, @AlexTugarev. If you believe, it should be handled on the git backend, just reassign it to me. Thanks!