video: start device event listener when device list is empty

This patch fix video device detection. Before device event listeners
would not start if a video device list is empty.

Change-Id: I5b320c1ae47b945d6f570e3cd2afcd6bd01dfdae

src/media/video/osxvideo/video_device_monitor_impl.mm

@@ -71,15 +71,10 @@ void VideoDeviceMonitorImpl::start()
     auto myVideoDevices = [[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo]
                            arrayByAddingObjectsFromArray:
                            [AVCaptureDevice devicesWithMediaType:AVMediaTypeMuxed]];
-    if ( [myVideoDevices count] == 0 )
-    {
-        JAMI_ERR("Can't find any suitable video device");
-        return;
-    }
-
     int deviceCount = [myVideoDevices count];
-    int ivideo;
-    for ( ivideo = 0; ivideo < deviceCount; ++ivideo )
+    if (deviceCount > 0)
+    {
+        for (int ivideo = 0; ivideo < deviceCount; ++ivideo)
         {
             AVCaptureDevice* avf_device = [myVideoDevices objectAtIndex:ivideo];
             printf("avcapture %d/%d %s %s\n", ivideo + 1,
@@ -92,6 +87,7 @@ void VideoDeviceMonitorImpl::start()
                 JAMI_ERR("%s", e.what());
             }
         }
+    }
 
     NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
     id deviceWasConnectedObserver = [notificationCenter addObserverForName:AVCaptureDeviceWasConnectedNotification