CURA-2079: Finish firmware upload process on errors

Looking at the old code shows that the download process was never
completely finished. The according function was only return'ed, but no
signal was emitted to the window to give the user the possibility to
close it again.

Optionally, it would be useful here to pass messages to the window
dialog to inform the user about problems.

However, this code is untested because:
1. I don't know where put my printers *.hex-file, when coding here with
my editor,
2. Have no idea how to reproduce the IO errors reported at JIRA, so
fingers crossed here.

Contributes to CURA-2079

plugins/USBPrinting/USBPrinterOutputDevice.py

@@ -182,7 +182,8 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
 
         if len(hex_file) == 0:
             Logger.log("e", "Unable to read provided hex file. Could not update firmware")
-            return 
+            self._updateFirmware_completed()
+            return
 
         programmer = stk500v2.Stk500v2()
         programmer.progressCallback = self.setProgress
@@ -197,6 +198,7 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
 
         if not programmer.isConnected():
             Logger.log("e", "Unable to connect with serial. Could not update firmware")
+            self._updateFirmware_completed()
             return 
 
         self._updating_firmware = True
@@ -206,15 +208,21 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
             self._updating_firmware = False
         except Exception as e:
             Logger.log("e", "Exception while trying to update firmware %s" %e)
-            self._updating_firmware = False
+            self._updateFirmware_completed()
             return
         programmer.close()
 
+        self._updateFirmware_completed()
+        return
+
+    ##  Private function which makes sure that firmware update process has completed/ended
+    def _updateFirmware_completed(self):
         self.setProgress(100, 100)
         self._firmware_update_finished = True
-
+        self.resetFirmwareUpdate(update_has_finished=True)
         self.firmwareUpdateComplete.emit()
-        self.firmwareUpdateChange.emit()
+        
+        return
 
     ##  Upload new firmware to machine
     #   \param filename full path of firmware file to be uploaded
@@ -227,8 +235,8 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
     def firmwareUpdateFinished(self):
         return self._firmware_update_finished
 
-    def resetFirmwareUpdateFinished(self):
-        self._firmware_update_finished = False
+    def resetFirmwareUpdate(self, update_has_finished = False):
+        self._firmware_update_finished = update_has_finished
         self.firmwareUpdateChange.emit()
 
     @pyqtSlot()