Fix: Update diff base to match old version history

When changing diff base in the "Old Version History"
(Change Screen) and then entering the Side-By-Side
view for a file, clicking back-button in the browser
(reentering the Change Screen) will cause the files
to be wrongly compared with 'Base' again.

Bug: Issue 1523
Change-Id: I6b519aa1230c21d8c6f0f034ed7616b65a994d7f
1 file changed