handle degenerate call to blitAntiRect

Bug: skia:8043
Change-Id: Ief3653a748a1e82bd5ca9df3dd7743797e0160e8
Reviewed-on: https://skia-review.googlesource.com/132086
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed