Set machine_extruder_count in sync with defined extruders

The registry checks if they are in sync and complains if they aren't. The extruder count is set back to default to 1 upon adding the machine.

Contributes to issue CURA-3497.

plugins/MachineSettingsAction/MachineSettingsAction.qml

@@ -375,6 +375,10 @@ Cura.MachineAction
                                         }
                                     }
                                     currentIndex: machineExtruderCountProvider.properties.value - 1
+                                    Component.onCompleted:
+                                    {
+                                        manager.setMachineExtruderCount(1);
+                                    }
                                     onActivated:
                                     {
                                         manager.setMachineExtruderCount(index + 1);