Fix rendering change descriptions without raw insert/delete counts.
Review Request #6778 — Created Jan. 15, 2015 and submitted
When rendering a change entry for a diff, the code attempts to get the total raw insert/delete line counts across all FileDiffs. If there are no FileDiffs for some reason, then this would end up crashing. We're now more careful to not assume these counts exist, and to use 0 as the value in this case.
Tested with faking the return value for the function.