Fix viewer crash with corrupted MSKPs

If an MSKP fails to load, fPlayer will be null, and viewer will crash
when switching backends.

Change-Id: I68b63da21c8f7c5726b3c5bbbdcb6c17018a63ac
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/510209
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
1 file changed