MWL#182: Explain running statements

- Code cleanup

sql/sql_class.h

@@ -1467,6 +1467,8 @@ public:
   THD *target_thd;
   THD *request_thd;
   
+  bool failed_to_produce;
+  
   select_result_explain_buffer *explain_buf;
 
   static void get_explain_data(void *arg);