Catch first file patch failed exception.
Catch first file patch failed exception.

Catch exception when first file diff fails to apply. This makes the view diff
display the "Diff currently unavailable" error message instead of just throwing
out the traceback onto screen.

Tested on local 1.7 beta 3 (dev) server.
Reviewed at http://reviews.reviewboard.org/r/3324/

chipx86/reviewboard,bkochendorfer/reviewboard,custode/reviewboard,chipx86/reviewboard,bkochendorfer/reviewboard,1tush/reviewboard,KnowNo/reviewboard,sgallagher/reviewboard,KnowNo/reviewboard,chipx86/reviewboard,1tush/reviewboard,1tush/reviewboard,1tush/reviewboard,1tush/reviewboard,davidt/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,1tush/reviewboard,davidt/reviewboard,reviewboard/reviewboard,bkochendorfer/reviewboard,reviewboard/reviewboard,KnowNo/reviewboard,beol/reviewboard,1tush/reviewboard,davidt/reviewboard,brennie/reviewboard,beol/reviewboard,KnowNo/reviewboard,bkochendorfer/reviewboard,chipx86/reviewboard,sgallagher/reviewboard,custode/reviewboard,custode/reviewboard,brennie/reviewboard,brennie/reviewboard,1tush/reviewboard,1tush/reviewboard,davidt/reviewboard,beol/reviewboard,custode/reviewboard,beol/reviewboard,brennie/reviewboard,sgallagher/reviewboard,sgallagher/reviewboard