[InstCombine] Fix InstCombinerImpl::foldICmpMulConstant for nsw and nuw mul with unsigned compare.

If we have both an nsw and nuw flag, we would see the nsw flag
first and only handle signed comparisons.

This patch ignores the nsw flag if the comparison isn't signed.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D143766