MDEV-37345 sequences and prelocking (11.4 version)

table->pos_in_table_list is problematic, it can become
dangled when an SP is reparsed. Let's avoid it and directly
prefer TABLEs where a sequence is ready for inserts.

followup for 516f68a

Author: vuvova

sql/sql_base.cc

@@ -2048,16 +2048,12 @@ bool open_table(THD *thd, TABLE_LIST *table_list, Open_table_context *ot_ctx)
         {
           int distance= ((int) table->reginfo.lock_type -
                          (int) table_list->lock_type) * 2;
-          TABLE_LIST *tl= thd->locked_tables_mode == LTM_PRELOCKED
-                      ? table->pos_in_table_list : table->pos_in_locked_tables;
           /*
-            note, that merge table children are automatically added to
-            prelocking set in ha_myisammrg::add_children_list(), but their
-            TABLE_LIST's are on the execution arena, so tl will be invalid
-            on the second execution. Let's just skip them below.
+            if we need a table for inserting, make sure it has
+            its internal tables (a.k.a. sequences) ready
           */
-          if (table_list->parent_l || !tl ||
-              table_list->for_insert_data != tl->for_insert_data)
+          if (table->internal_tables &&
+              table_list->for_insert_data == !table->internal_tables->table)
             distance|= 1;
 
           /*