abort if glyph metrics fall outside safe rect

Caught this while debugging a fuzz from Kevin.

Haven't seen this on Windows, but seems like it's got roughly the same
possible issue.

Change-Id: I5e1c7328890492b3f3295af27757e456e26f9cbf
Reviewed-on: https://skia-review.googlesource.com/55760
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
2 files changed