Add some extra checks for video stream and track

app/src/RoomClient.js

@@ -1081,7 +1081,7 @@ export default class RoomClient
 			logger.debug(
 				'changeWebcam() | new selected webcam [device:%o]',
 				device);
-
+			if (this._webcamProducer && this._webcamProducer.track)
 				this._webcamProducer.track.stop();
 
 			logger.debug('changeWebcam() | calling getUserMedia()');
@@ -1094,14 +1094,21 @@ export default class RoomClient
 						...VIDEO_CONSTRAINS[resolution]
 					}
 				});
-
+			if (stream){
 				const track = stream.getVideoTracks()[0];
-
+				if (track) {
 					await this._webcamProducer.replaceTrack({ track });
 	
 					store.dispatch(
 						producerActions.setProducerTrack(this._webcamProducer.id, track));
 							
+				} else {
+					logger.warn('getVideoTracks Error: First Video Track is null')
+				}
+	
+			} else {
+				logger.warn ('getUserMedia Error: Stream is null!') 
+			}
 			store.dispatch(settingsActions.setSelectedWebcamDevice(deviceId));
 
 			await this._updateWebcams();