Bug#31630 debug assert with explain extended select ... from i_s

added 'in_rows' column value for 'describe extended' for the case 
when 'describe' handles I_S table

mysql-test/r/information_schema.result

@@ -1604,4 +1604,9 @@ select * from `information_schema`.`VIEWS` where `TABLE_SCHEMA` = NULL;
 TABLE_CATALOG	TABLE_SCHEMA	TABLE_NAME	VIEW_DEFINITION	CHECK_OPTION	IS_UPDATABLE	DEFINER	SECURITY_TYPE	CHARACTER_SET_CLIENT	COLLATION_CONNECTION
 select * from `information_schema`.`VIEWS` where `TABLE_NAME` = NULL;
 TABLE_CATALOG	TABLE_SCHEMA	TABLE_NAME	VIEW_DEFINITION	CHECK_OPTION	IS_UPDATABLE	DEFINER	SECURITY_TYPE	CHARACTER_SET_CLIENT	COLLATION_CONNECTION
+explain extended select 1 from information_schema.TABLES;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	TABLES	ALL	NULL	NULL	NULL	NULL	NULL	NULL	Skip_open_table; Scanned all databases
+Warnings:
+Note	1003	select 1 AS `1` from `information_schema`.`TABLES`
 End of 5.1 tests.

mysql-test/t/information_schema.test

@@ -1232,4 +1232,9 @@ select * from `information_schema`.`TRIGGERS` where `EVENT_OBJECT_TABLE` = NULL;
 select * from `information_schema`.`VIEWS` where `TABLE_SCHEMA` = NULL;
 select * from `information_schema`.`VIEWS` where `TABLE_NAME` = NULL;
 
+#
+# Bug#31630 debug assert with explain extended select ... from i_s
+#
+explain extended select 1 from information_schema.TABLES;
+
 --echo End of 5.1 tests.

sql/sql_select.cc

@@ -15819,6 +15819,10 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       /* Add "rows" field to item_list. */
       if (table_list->schema_table)
       {
+        /* in_rows */
+        if (join->thd->lex->describe & DESCRIBE_EXTENDED)
+          item_list.push_back(item_null);
+        /* rows */
         item_list.push_back(item_null);
       }
       else