Fix bugs related to SkMatrixConvolutionImageFilter in repeat mode

This should fix most of the fuzzer complaints

Change-Id: I47a616e78b47bd162cbef647b03f5c1f23017c6f
Reviewed-on: https://skia-review.googlesource.com/129165
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed