Don't try to send empty g-code lines

plugins/USBPrinting/USBPrinterOutputDevice.py

@@ -19,8 +19,8 @@ from PyQt5.QtCore import QUrl, pyqtSlot, pyqtSignal, pyqtProperty
 from UM.i18n import i18nCatalog
 catalog = i18nCatalog("cura")
 
-class USBPrinterOutputDevice(PrinterOutputDevice):
 
+class USBPrinterOutputDevice(PrinterOutputDevice):
     def __init__(self, serial_port):
         super().__init__(serial_port)
         self.setName(catalog.i18nc("@item:inmenu", "USB printing"))
@@ -559,6 +559,12 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
         if ";" in line:
             line = line[:line.find(";")]
         line = line.strip()
+
+        # Don't send empty lines
+        if line == "":
+            self._gcode_position += 1
+            return
+
         try:
             if line == "M0" or line == "M1":
                 line = "M105"  # Don't send the M0 or M1 to the machine, as M0 and M1 are handled as an LCD menu pause.

plugins/USBPrinting/USBPrinterOutputDeviceManager.py

@@ -238,7 +238,6 @@ class USBPrinterOutputDeviceManager(QObject, OutputDevicePlugin, Extension):
         except KeyError:
             Logger.log("w", "Connection state of %s changed, but it was not found in the list")
 
-
     @pyqtProperty(QObject , notify = connectionStateChanged)
     def connectedPrinterList(self):
         self._usb_output_devices_model = ListModel()