Fix for bug#23379 "wrong time value in SHOW PROCESSLIST"

The value taken to be shown in SHOW PROCESSLIST is not
initialized when THD is created and will be random for
unauthenticated connections.

To the documentor: Random value, instead of NULL, was shown,
in SHOW PROCESSLIST for still non-authenticated connections.

sql/sql_class.cc

@@ -181,6 +181,7 @@ THD::THD()
   // Must be reset to handle error with THD's created for init of mysqld
   lex->current_select= 0;
   start_time=(time_t) 0;
+  time_after_lock=(time_t) 0;
   current_linfo =  0;
   slave_thread = 0;
   variables.pseudo_thread_id= 0;