MDEV-28030 row_discard_tablespace_for_mysql() can unlock data dictionary...

MDEV-28030 row_discard_tablespace_for_mysql() can unlock data dictionary without locking data dictionary

- row_discard_tablespace_for_mysql() could unlock the data dictionary lock without locking it in the first place.

storage/innobase/row/row0mysql.cc

@@ -2495,7 +2495,8 @@ dberr_t row_discard_tablespace_for_mysql(dict_table_t *table, trx_t *trx)
         fts_optimize_add_table(table);
       }
       trx->rollback();
-      row_mysql_unlock_data_dictionary(trx);
+      if (trx->dict_operation_lock_mode)
+        row_mysql_unlock_data_dictionary(trx);
       return err;
     }
   }