Fails to discard unstaged changes - cannot read property 'filename' of undefined

[lresende]

Description

This is using 0.23.0 but I believe I saw similar behavior on 0.22.x as well.

[ianhi]

on master I get this error: (edit: in retrospect the difference error messages is probably a firefox vs chrome difference)

I think two things are happening:

1. options is being used outside of the check for if it is undefined here:
   

   jupyterlab-git/src/model.ts

   Line 399 in 582ef5a

   this._revertFile(options.filename);

2. discard all changes doesn't use the options to specify the files that are being discarded. instead it just run git checkout. This will revert the changes but if there are open editors then they won't be updated to reflect the state on disk. (I think this is also a bug)

[ianhi]

Changing the revertFile lines to:

        } else if (body.filename) {
          this._revertFile(body.filename);
        }

fixes the error, but there will still be the issue that open editors aren't updated when doing revert all changes