Fixes the case where someone uses the kF16ColorType flag to saveLayer
but the GPU doesn't support F16 render targets.
Follow-up to https://skia-review.googlesource.com/c/skia/+/243041,
which improved the quality of the savelayer_f16 GM on most GPUs, but
removed the final draw on the GPUs that can't respect the flag.
Change-Id: I03dac6b2370bc9117c082f6c5c9b14e84b631339
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/243156
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
c248659c19