MDEV-22339 - Assertion `str_length < len' failed

When acquiring SNW/SNRW/X MDL lock DDL/admin statements may abort pending
thr lock in concurrent connection with open HANDLER (or delayed insert
thread).

This may lead to a race condition when table->alias is accessed
concurrently by such threads. Either assertion failure or memory leak
is a practical consequence of this race condition.

Specifically HANDLER is opening a table and issuing alias.copy(), while
DDL executing get_lock_data()/alias.c_ptr()/realloc()/realloc_raw().

Fixed by perforimg table->init() before it is published via
thd->open_tables.

mysql-test/suite/stress/r/misc.result

+#
+# MDEV-22339 - Assertion `str_length < len' failed in
+#              Binary_string::realloc_raw
+#
+CREATE TABLE t1(a INT) ENGINE=MyISAM;
+connect con1, localhost, root;
+disconnect con1;
+connection default;
+DROP TABLE t1;

mysql-test/suite/stress/t/misc.test

+--echo #
+--echo # MDEV-22339 - Assertion `str_length < len' failed in
+--echo #              Binary_string::realloc_raw
+--echo #
+CREATE TABLE t1(a INT) ENGINE=MyISAM;
+connect con1, localhost, root;
+let $i=1000;
+disable_query_log;
+disable_result_log;
+while ($i)
+{
+  connection default;
+  HANDLER t1 OPEN;
+  send SELECT * FROM t1, t1 t1a1over8, t1 t1a2over8, t1 t1a3over8, t1 t1a4over8, t1 t1a5over8, t1 t1a6over8;
+
+  connection con1;
+  send REPAIR TABLE t1;
+
+  connection default;
+  reap;
+  HANDLER t1 CLOSE;
+
+  connection con1;
+  reap;
+  dec $i;
+}
+enable_query_log;
+enable_result_log;
+disconnect con1;
+
+connection default;
+DROP TABLE t1;

sql/sql_base.cc

@@ -1675,6 +1675,7 @@ bool open_table(THD *thd, TABLE_LIST *table_list, Open_table_context *ot_ctx)
     {
       table= best_table;
       table->query_id= thd->query_id;
+      table->init(thd, table_list);
       DBUG_PRINT("info",("Using locked table"));
       goto reset;
     }
@@ -1959,12 +1960,13 @@ bool open_table(THD *thd, TABLE_LIST *table_list, Open_table_context *ot_ctx)
   }
 
   table->mdl_ticket= mdl_ticket;
+  table->reginfo.lock_type=TL_READ;		/* Assume read */
+
+  table->init(thd, table_list);
 
   table->next= thd->open_tables;		/* Link into simple list */
   thd->set_open_tables(table);
 
-  table->reginfo.lock_type=TL_READ;		/* Assume read */
-
  reset:
   /*
     Check that there is no reference to a condition from an earlier query
@@ -1989,8 +1991,6 @@ bool open_table(THD *thd, TABLE_LIST *table_list, Open_table_context *ot_ctx)
   }
 #endif
 
-  table->init(thd, table_list);
-
   DBUG_RETURN(FALSE);
 
 err_lock: