Fix / prevent camera switch if no second camera

vector/src/main/java/im/vector/riotx/features/call/WebRtcPeerConnectionManager.kt

@@ -736,6 +736,7 @@ class WebRtcPeerConnectionManager @Inject constructor(
 
     fun switchCamera() {
         Timber.v("## VOIP switchCamera")
+        if (!canSwitchCamera()) return
         if (currentCall != null && currentCall?.mxCall?.state is CallState.Connected && currentCall?.mxCall?.isVideoCall == true) {
             videoCapturer?.switchCamera(object : CameraVideoCapturer.CameraSwitchHandler {
                 // Invoked on success. |isFrontCamera| is true if the new camera is front facing.