Fix crash if Rive file is missing.

Change-Id: I3910025b527587208bfbc592e45ac3ccb20a738d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/299381
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: John Stiles <johnstiles@google.com>
1 file changed