Fix null dereference in ~PromiseImageInfo.

While working on an unrelated fuzzing task, I noticed in the logs that
~PromiseImageInfo was crashing on a null dereference while the fuzzers
were doing smoke checks. It looks like fuzzer was being detected as
"broken" and presumably is not being run: http://screen/AKPKmyx7mHJ5nir

This CL should resolve the null dereference, but I don't know if this
indicates a deeper problem.

Bug: skia:12851
Change-Id: I4a44891783504372f28ab4b320c01a14df0892a7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/497436
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
1 file changed