Allow M42 M with other parameters (#17744)

Marlin/src/gcode/control/M42.cpp

       #ifdef INPUT_PULLDOWN
         case 3: pinMode(pin, INPUT_PULLDOWN); break;
       #endif
-      default: SERIAL_ECHOLNPGM("Invalid Pin Mode");
+      default: SERIAL_ECHOLNPGM("Invalid Pin Mode"); return;
     }
-    return;
   }
 
   if (!parser.seenval('S')) return;