codec/avcodec/vaapi-x11.c: signal use of invalid pictures

The pictures used by vaapi-x11 vout are not valid vlc pictures, but merely
a placeholder for VASurfaceID.

modules/codec/avcodec/vaapi_x11.c

@@ -224,7 +224,7 @@ int OpenVaapiX11 (vlc_object_t *obj)
 
     /* */
     vout_display_info_t info = vd->info;
-    info.has_pictures_invalid = false;
+    info.has_pictures_invalid = true;
     info.has_event_thread = false;
 
     /* Setup vout_display_t once everything is fine */