gp4par: fixed null deref during DRC if POR is not used in the specific netlist
gp4par: fixed null deref during DRC if POR is not used in the specific netlist

azonenberg/openfpga,azonenberg/openfpga,rqou/openfpga,azonenberg/openfpga,azonenberg/openfpga,rqou/openfpga,rqou/openfpga,rqou/openfpga,azonenberg/openfpga,rqou/openfpga