MDEV-35852 : ASAN heap-use-after-free in WSREP_DEBUG after INSERT DELAYED

Problem was that in case of INSERT DELAYED thd->query() is
freed before we call trans_rollback where WSREP_DEBUG
could access thd->query() in wsrep_thd_query().

Fix is to reset thd->query() to NULL in delayed_insert
destructor after it is freed. There is already
null guard at wsrep_thd_query().

Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>

sql/sql_insert.cc

@@ -2421,6 +2421,7 @@ public:
     delayed_insert_threads--;
 
     my_free(thd.query());
+    thd.reset_query_inner();
     thd.security_ctx->user= 0;
     thd.security_ctx->host= 0;
   }