Harden runtime shader/colorfilter CreateProc against bad child counts

Change-Id: I7d2f32a8cd4d373afddb2f1bfdb736e2979ec000
Bug: oss-fuzz:19883
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/270637
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed