Fixed es_format_Clean (when called multiple times with the same es_format).

include/vlc_es.h

@@ -294,5 +294,7 @@ static inline void es_format_Clean( es_format_t *fmt )
         }
         free(fmt->p_extra_languages);
     }
+    fmt->i_extra_languages = 0;
+    fmt->p_extra_languages = NULL;
 }
 #endif