util/fossilize_db: don't use check_files_opened_successfully for foz_prepare

The check function will free the db or the file if the other is NULL,
however, in this case db and the file are passed to foz_destroy, which
will also free them. This results in a double free. Instead, check that
either is NULL, and then goto the error case to ensure proper cleanup.

Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29881>

src/util/fossilize_db.c

@@ -519,7 +519,7 @@ foz_prepare(struct foz_db *foz_db, char *cache_path)
       free(filename);
       free(idx_filename);
 
-      if (!check_files_opened_successfully(foz_db->file[0], foz_db->db_idx))
+      if (foz_db->file[0] == NULL || foz_db->db_idx == NULL)
          goto fail;
 
       if (!load_foz_dbs(foz_db, foz_db->db_idx, 0, false))