Make ManagedBackendTexture fail on invalid GrBackendTexture

Makes it more sensible.

A bunch of call sites we're already written to expect this. Update
some others.

Change-Id: I77c28045ebf01e6aa9d92d2ebc37287604ec10c9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/332544
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
6 files changed