Virtual: Report invalid extruders on serial
Virtual: Report invalid extruders on serial

For testing #2302

Jaesin/OctoPrint,foosel/OctoPrint,Jaesin/OctoPrint,foosel/OctoPrint,Jaesin/OctoPrint,foosel/OctoPrint,Jaesin/OctoPrint,foosel/OctoPrint