read_verilog pin { pin ( seg fault

Signed-off-by: James Cherry <cherry@parallaxsw.com>

liberty/LibertyReader.cc

@@ -2977,6 +2977,7 @@ LibertyReader::endPorts()
 {
   // Capacitances default based on direction so wait until the end
   // of the pin group to set them.
+  if (ports_) {
     for (LibertyPort *port : *ports_) {
       if (in_bus_ || in_bundle_) {
         // Do not clobber member port capacitances by setting the capacitance
@@ -2992,6 +2993,7 @@ LibertyReader::endPorts()
     }
     ports_ = nullptr;
     port_group_ = nullptr;
+  }
 }
 
 void