Fix an annoying unicode comparison warning.
Review Request #6254 — Created Aug. 21, 2014 and submitted
If a given patch file isn't coercible to unicode, it would cause a
UnicodeWarning when comparing it to the empty string. I've replaced this test
with a truthy-test, which won't try to convert the arguments.
Ran unit tests.
Tool: Pyflakes Processed Files: reviewboard/diffviewer/diffutils.py Tool: PEP8 Style Checker Processed Files: reviewboard/diffviewer/diffutils.py