Fix prefix/postfix mixup discovered by fuzzer.

Change-Id: I8b70f456d1a659e46600bbad40b5bcadd08e8edf
Bug: oss-fuzz:26759
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/330743
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
1 file changed