Checkpoint diff can fail and can confuse the user

[abstrakt8]

Issue

Occasionally the checkpoint diff fails (we have a ticket in the backend) and we get an unhandled exception at the following line of code:

https://github.com/playcanvas/editor/blob/0ce6862bd08392cc0f0a54e8911cb394df717100/src/editor/pickers/version-control/picker-version-control.ts#L948

TypeError: Cannot read properties of undefined (reading 'numConflicts')

The issue is that we don't surface this issue to the user and the version control modal does not change its state - it still shows "Showing changes" while nothing was shown. The user has to open up the console to check that something went wrong.