MDEV-10957: Assertion failure when dropping a myisam table

... with wsrep_replicate_myisam enabled

Internal updates to system statistical tables could wrongly
trigger an additional total-order replication if wsrep_repli
-cate_myisam is enabled.
Fixed by adding a check to skip total-order replication for
stat tables.

sql/sql_base.cc

@@ -4068,6 +4068,7 @@ restart:
       (*start)                                 &&
       (*start)->table                          &&
       (*start)->table->file->ht == myisam_hton &&
+      !is_stat_table((*start)->db, (*start)->alias) &&
       sqlcom_can_generate_row_events(thd)      &&
       thd->get_command() != COM_STMT_PREPARE)
   {