Fix for over-enthusiastic pruning of expressions.
Fix for over-enthusiastic pruning of expressions.

The minimum width for expressions containing a literal number was
being incorrectly calculated, leading to loss of information in
some circumstances.

CastMi/iverilog,themperek/iverilog,CastMi/iverilog,themperek/iverilog,CastMi/iverilog,themperek/iverilog