[graphite] Add shader error handling

Change-Id: I21743290128140bef729eef967e841a65f9fdc67
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/482702
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
3 files changed