followup #406: fix diffing from commits in history view for code files and notebooks

ref #406

With #406 merged in, at least some files can be diffed successfully from any commit in the history view. However, trying to diff any code file (.py, ‘.ts’, etc) results in:

and trying to diff an .ipynb notebook produces a similar, but slightly different error:

[telamonian]

This is fixed as of latest master (14e66f1b99f5a6e553253d72d67bcfb26c6d3b1c)

[telamonian]

I was originally seeing the diffing issue with all notebooks from the history. After the last couple of rebuilds, though, I can’t reproduce that particular error.

However, what I do see now is that notebooks added in a repo’s very first commit:

produce the same diff error that I was seeing before: