check if stream failed

If so, index might be uninitialized, so don't use it

Bug: skia:
Change-Id: Icccf6c796cf73317f10c80d6f7523479662c401f
Reviewed-on: https://skia-review.googlesource.com/151221
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed