Make unified diffs of images show the images again

Since 6963c5fc64bdec4253a08b43e9e0cfc5e67f8f0b, the image showing
block was wrapped in a guard against binary patches. So images were no
longer shown. We move the guard against binary patches to the part
that renders the text diff, and thereby allow to show images again.

Change-Id: Ib09aa6a694f42cb789a4e499f90a1d5430b4fd60
1 file changed