MDEV-22263: main.func_debug fails on a valgrind build with wrong result

Patches of interest:374dae3ecc49, 374dae3ecc

mysql-test/main/func_debug.result

@@ -1671,6 +1671,6 @@ a
 2
 9
 Warnings:
-Note	1105	DBUG: Item_subselect::exec (select max(`test`.`t1`.`a`) from `test`.`t...
+Note	1105	DBUG: Item_subselect::exec (select max(`test`.`t1`.`a`) from `test`.`t1`)
 DROP TABLE t1;
 SET SESSION debug_dbug="-d,Item_subselect";

sql/item_subselect.cc

@@ -717,7 +717,7 @@ bool Item_subselect::exec()
 
     push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
        ER_UNKNOWN_ERROR, "DBUG: Item_subselect::exec %.*s",
-       print.length(),print.ptr());
+       print.length(),print.c_ptr());
   );
   /*
     Do not execute subselect in case of a fatal error