oembed iframe: return null as it was before refactoring when no src i…

…n Iframe

lib/plugins/system/oembed/oembed.js

@@ -83,7 +83,7 @@ function _getOembedIframe(oembed) {
             _iframe = null;
         }
 
-        oembed._iframe = {..._iframe};
+        oembed._iframe = _iframe ? {..._iframe} : null;
     }    
 
     return oembed._iframe;