SkUtils: safe SkUTF16_NextUnichar

Change-Id: Ief70f3055d9612c8934ede967c1048dd7fcb102a
Reviewed-on: https://skia-review.googlesource.com/135705
Commit-Queue: Hal Canary <halcanary@google.com>
Auto-Submit: Hal Canary <halcanary@google.com>
Reviewed-by: Herb Derby <herb@google.com>
3 files changed