handle empty candidate field

raspberry/roberto/camera/camera_gstreamer_webrtc.py

@@ -158,6 +158,9 @@ class WebRTCCamera(Thread):
     def handle_ice(self, ice, client_sid):
         print("handle_ice")
         candidate = ice['candidate']
+        if not candidate or candidate == '':
+            print("candidate string is empty")
+            return
         sdpmlineindex = ice['sdpMLineIndex']
         self._peers[client_sid]['webrtc'].emit('add-ice-candidate', sdpmlineindex, candidate)