If the format passed to MakeValidSize is invalid, there
is potential for a mod by 0 which can result in a crash.

Test: Verify no crash when format is invalid.

Bug: b/182823289
Change-Id: I7f538be5d984070984f5581a5cc7ea47264109f4
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2780557Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Doug Horn <doughorn@google.com>