improve previewer

www/js/beauty.js

@@ -224,7 +224,7 @@ if ($('#pr-player').length > 0 && typeof(videojs) != 'undefined') {
 
     var mc_video_id = '';
     var tryToGetVideoSnapshot = function() {
-        if (noSnapVideos.length == 0) {return false;}
+        if (noSnapVideos.length == 0 || mc_video_id) {return false;}
 
         var videoItem = noSnapVideos.shift();
         mc_video_id = videoItem.id;