Automatically switch from empty side-by-side to unified view

If the user visits a sidebyside view location, but we come up with
no file hunks to display (e.g. because it really is binary) then
we switch them to the unified viewer, which can show the headers
from the diff.

Bug: GERRIT-193
Signed-off-by: Shawn O. Pearce <sop@google.com>
1 file changed