[fontations] Test to fail to compare gracefully

Avoid crashing in the fontations_compare_ft_* tests when using 16bpp
formats or formats like PDF which don't have pixels in their canvas.

Change-Id: I0f4c84afc60b4710f8dcae7828b75240d54dffd0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/851777
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Ben Wagner <bungeman@google.com>
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>
1 file changed