Use self._camera_active to detect whether we should show the camera

Because the camera timer is whether we should request the camera.

Contributes to issue CURA-4376.

cura/PrinterOutputDevice.py

@@ -242,8 +242,8 @@ class PrinterOutputDevice(QObject, OutputDevice):
 
     @pyqtSlot()
     def stopCamera(self):
-        self._camera_active = False
         self._stopCamera()
+        self._camera_active = False
 
     def _stopCamera(self):
         Logger.log("w", "_stopCamera is not implemented by this output device")

plugins/UM3NetworkPrinting/NetworkPrinterOutputDevice.py

@@ -334,7 +334,7 @@ class NetworkPrinterOutputDevice(PrinterOutputDevice):
         else: #Camera wasn't even running. Don't try to stop it or you'll get a segfault.
             return
 
-        if self._image_reply:
+        if self._camera_active:
             try:
                 self._image_reply.abort()
                 self._image_reply.downloadProgress.disconnect(self._onStreamDownloadProgress)