abort blur if the sigma is too small

Bug: oss-fuzz:6375
Change-Id: I8f21ea05b44f2ed6fdcdfe2573ac9415f238d833
Reviewed-on: https://skia-review.googlesource.com/107784
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Herb Derby <herb@google.com>
2 files changed