Correct FreeType palette setup.

Use the override index as intended instead of the index into the
override list as the palette entry index to override. Correct the bounds
check on the override index. Modify an existing test to exercise this.

Bug: skia:12576
Change-Id: Ide8327ff0536eee252c6a83e997ad540a98ba957
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/510596
Auto-Submit: Ben Wagner <bungeman@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed