title: Issue: Glib-Gobject-warning **: cannot register existing type 'GDKDisplayManager'
body: <p>I've designed a interface with pyqt and opencv python to my raspberry, so there's no problem when I run a basic test to open the camera  ( cv2.imshow('test',frame) this is too basic is just to check if my camera is working) and yeah the camera open successfully but the problem occurs when I try to open the camera within my interface created on pyqt5, because it launches a few errors but the main is 
     <code>Glib-Gobject-Warning **: cannot register existing type 'GDKDisplayManager'</code></p>
  
  <p>Full Error:</p>
  
  <pre><code>Glib-Gobject-Warning **: cannot register existing type 'GDKDisplayManager'
  Glib-critical **: g_once_init_leave: assertion 'result != 0 ' failed
  Glib-Gobject-CRITICAL **:g_object_new: assertion 'G_TyPE_IS_OBJECT(Object_type)'fail
  Glib-GObject-WARNING **: invalid (null) pointer instance
  Glib-GObject-CRTICAL **: g_signal_connect_data: assertion 'G_TYPE_CHECK_INSTANCE(instance)'failed
  Glib_GObject-WARNING **: cannot register existing type 'GdkDisplay'
  Glib-critical **: g_once_init_leave: assertion 'result != 0 ' failed
  Glib-Gobject-CRITICAL **: g_type_register_static: assertion 'parent_Type &gt; 0'failed
  Glib-critical **: g_once_init_leave: assertion 'result != 0 ' failed
  Glib-Gobject-CRITICAL **:g_object_new: assertion 'G_TyPE_IS_OBJECT(Object_type)'failed
  </code></pre>
  
  <p>This is the function which is opening the camera</p>
  
  <pre><code>def OpenCamera(self):
      self.setup_CameraSettings()       
      cap = cv2.VideoCapture(self.CameraSource) # video capture source camera (Here webcam of laptop) 
      cap.set(3, self.Resolution_x) # set the resolution
      cap.set(4, self.Resolution_y)
      cap.set(cv2.CAP_PROP_AUTOFOCUS, 0) # turn the autofocus off
      focus = self.Focus  # min: 0, max: 255, increment:5
      cap.set(cv2.CAP_PROP_FOCUS, focus)
  
      ret,frame = cap.read() # return a single frame in variable `frame`
  
      if ret== True:            
          cv2.imshow('Settings Test',frame)
          cv2.waitKey(0)
          cv2.destroyAllWindows() 
      else:
          self.popUp_Message('Camera Unplugged')
  </code></pre>
  
  <p>This code is running successfully on my PC so the problem is not in the function, I think is about PyQt at my raspberry pi </p>