Limit maximum sigma to avoid overflows

Limit the maximum sigma to avoid overflowing the blur calculation,
and more importantly to limit the size of buffers.

I checked that this failed on my linux box, and this CL fixes
the problem.

BUG=chromium:768294

Change-Id: I7ed14acc47f546db9c00c78c148a898459852a9f
Reviewed-on: https://skia-review.googlesource.com/50920
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
1 file changed