Changing revisions in source view encodes the url and shows a blank screen

Steps to reproduce:

1. Go to the source view of a file for a revision that doesn't exist (the file must be in a subdirectory, e.g. /a/file, not /file)
2. Change the revision using the dropdown

Expected: The file is shown at the new revision

Actual: There is a blank screen

This seems to be caused by the URL being encoded when it shouldn't be. i.e. it navigates to /projects/PROJECT_KEY/repos/REPO_SLUG/browse/path%2Fto%2Ffile?at=refs%2Fheads%2Fmaster and the '/' from the file path are encoded when they shouldn't be