Prior to this commit, this code was assumed that underflow testing on partial numeric conversion would only be used when the source type is a signed integer and the dest type has a smaller width. But this can also happen when the dest type has a greater or equal width when the dest type is unsigned, because all negative numbers are treated as underflow in that case.
This commit fixes the issue by implementing that case.
Prior to this commit, this code was assumed that underflow testing on partial numeric conversion would only be used when the source type is a signed integer and the dest type has a smaller width. But this can also happen when the dest type has a greater or equal width when the dest type is unsigned, because all negative numbers are treated as underflow in that case.
This commit fixes the issue by implementing that case.