Don't replace parameter overrides that did not evaluate.
Don't replace parameter overrides that did not evaluate.

Trying to replace a parameter override that did not evaluate
correctly can lead to a crash, so just skip the substitution.

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