Ignore system tasks/functions NULL arguments in @* calculation.
Ignore system tasks/functions NULL arguments in @* calculation.

System tasks and functions can be defined to have NULL arguments.
This patch makes the @* sensitivity list calculation skip these
NULL (constant) arguments.

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