Avoid underflow in modulo in loops

Just like https://review.skia.org/1247316 but modulo instead of div

Change-Id: I4981f81afffc24d928c34e940bfedf83fa7912ab
Bug: oss-fuzz:519154489
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1253418
Commit-Queue: Kaylee Lubick <kjlubick@google.com>
Reviewed-by: Jorge Betancourt <jmbetancourt@google.com>
Commit-Queue: Jorge Betancourt <jmbetancourt@google.com>
Auto-Submit: Kaylee Lubick <kjlubick@google.com>