Don't crash in aaflags GM if context is abandoned

Change-Id: I5683c2f7c0fb19b5e3fb7eab599651a3fe3eab3f
Reviewed-on: https://skia-review.googlesource.com/158823
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed