fix buffer overflow

The other side of this branch also reads too many bytes,
8 when only 4 are allowed.

Bug: oss-fuzz:17829
Change-Id: I3fe4a9e39acf77abacbae9ab892f1d0794a411a8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/245184
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed