Fixed another division by zero error in skslc

You'd think by now it would have occurred to me that mod is also a kind
of division.

BUG=skia:6087

Change-Id: I5128d09db94d06f10762ad5c23df32551c5e5855
Reviewed-on: https://skia-review.googlesource.com/6607
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
1 file changed