Only checksum and query a valid descriptor

Bug: oss-fuzz:19549

Change-Id: I941470cfa31c46b3e92cf53877efd2da8d181c01
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/260896
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
1 file changed