Another attempt to fix the valgrind warning in SHOW PROCESSLIST

(event_bugs.test)


sql/event_data_objects.cc:
  SHOW PROCESSLIST tries to read thd->query without a mutex.
  If we do not reset it, it points to free()d contents of stack variable
  sp_sql.

sql/event_data_objects.cc

@@ -1900,6 +1900,9 @@ end:
   thd->lex->unit.cleanup();
   thd->end_statement();
   thd->cleanup_after_query();
+  /* Avoid races with SHOW PROCESSLIST */
+  thd->query_length= 0;
+  thd->query= NULL;
 
   DBUG_PRINT("info", ("EXECUTED %s.%s  ret: %d", dbname.str, name.str, ret));