VAAPI-XCB: extra handling in error path

- subpicture_cache_destroy() set cache pointer to NULL
- CopyPictureToVAImage() invalidate image members

modules/codec/avcodec/vasub.c

@@ -144,6 +144,7 @@ static void subpicture_cache_destroy(vasubpicture_cache_t *cache)
     assert(cache->image.image_id == VA_INVALID_ID);
 
     free(cache);
+    cache = NULL;
 }
 
 unsigned int cache_GetCacheID(const subpicture_cache_t *cache)
@@ -268,7 +269,12 @@ static int CopyPictureToVAImage(vlc_object_t *obj, vlc_va_conn_t *vaconn,
     status = vaCreateImage(vaconn->p_display, fmt,
                            pic->format.i_width, pic->format.i_height, image);
     if (status != VA_STATUS_SUCCESS)
+    {
+        msg_Err(obj, "failed to creating image (%d)", status);
+        image->image_id = VA_INVALID_ID;
+        image->buf = VA_INVALID_ID;
         return VLC_EGENERIC;
+    }
 
     /* Sanity checks */
     if ((image->image_id == VA_INVALID_ID) ||