Previously there were times when binary data from an image diff would
display. This change adds a check in the diff processor for image diffs
and does not display anything other than the file line in that case.
This change also addresses an issue where the label is calculated too
soon. The image size (if it exists) is supposed to be included as part
of the label, but often this was calculated before the image was done
rendering, so it didn't display.
Bug: Issue 5887
Change-Id: I9cd1ad0c3f2603492d7d84892147bd6852bbae29
7fe6a3b4cc