End color analysis early when color becomes unknown

Bug: skia:
Change-Id: Ifce6f002336ccabf19dbaeb3fa8b40eae6acca19
Reviewed-on: https://skia-review.googlesource.com/c/175990
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
2 files changed