Issue Summary

The commit selectors become stuck in a loading state for the source view diff of a file with only the initial commit.

It can also occur in a more edge case (in any file) - when the user manually loads the URL comparing the same commits (ie: diff1=12345678&diff2=12345678)

Steps to Reproduce

1. Navigate to the source view for a file with only the initial commit
2. Select diff from the dropdown
3. Click on one of the commit selectors

Expected Results

The commit selectors should load

Actual Results

The commit selectors become stuck in a loading/spinning state 

Workaround

In both possible scenarios, a diff (if even possible) is not useful since there is only 1 commit. The same information can be found by looking at the source.