[TypePromotion] Fix another case for sext vs zext in promoted constant.

If the SafeWrap operation is a subtract, we negated the constant
to treat the subtract as an addition. The sext was based on the
operation being addition. So we really need to do (neg (sext (neg C)))
when promoting the constant. This is equivalent to (sext C) for
every value of C except the min signed value. For min signed value
we need to do (zext C) instead.

Fixes PR55490.

Differential Revision: https://reviews.llvm.org/D125653