libobs/media-io: Fix bug (skipped frames including lagged frames)

The skipped frame count (dropped frames due to encoding being
overloaded) would erroneously include lagged frames (dropped frames due
to render stalls).  This will make diagnosing actual issues a user might
be having a bit easier.

libobs/media-io/video-io.c

@@ -176,7 +176,6 @@ static void *video_thread(void *param)
 		profile_start(video_thread_name);
 		while (!video->stop && !video_output_cur_frame(video)) {
 			video->total_frames++;
-			video->skipped_frames++;
 		}
 
 		video->total_frames++;
@@ -404,6 +403,7 @@ bool video_output_lock_frame(video_t *video, struct video_frame *frame,
 	pthread_mutex_lock(&video->data_mutex);
 
 	if (video->available_frames == 0) {
+		video->skipped_frames += count;
 		video->cache[video->last_added].count += count;
 		locked = false;