Add some nullchecks to GrTriangulator

* Perform some nullchecks to satisfy the fuzzer, ensuring that we do not dereference a nullptr

Change-Id: I466bf1afbe6801dc25702aea95fb8fcf3f88ce51
Bug: https://crbug.com/1470494
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/738159
Auto-Submit: Nicolette Prevost <nicolettep@google.com>
Commit-Queue: Nicolette Prevost <nicolettep@google.com>
Reviewed-by: Herb Derby <herb@google.com>
1 file changed