InnoDB: restore thd->proc_info in innobase_reset_background_thd()

mysql-test/suite/innodb/r/purge_thread_shutdown.result

@@ -3,11 +3,11 @@ insert t1 values (1),(2),(3),(4);
 delete from t1 where a=1;
 select user,state from information_schema.processlist order by 2;
 user	state
-system user	
-system user	
-system user	
-system user	
 root	Filling schema table
+system user	InnoDB purge coordinator
+system user	InnoDB purge worker
+system user	InnoDB purge worker
+system user	InnoDB purge worker
 system user	InnoDB shutdown handler
 set global debug_dbug='+d,only_kill_system_threads';
 connect con1, localhost, root;

storage/innobase/handler/ha_innodb.cc

@@ -1746,8 +1746,9 @@ innobase_reset_background_thd(MYSQL_THD thd)
 	ut_ad(THDVAR(thd, background_thread));
 
 	/* background purge thread */
+	const char *proc_info= thd_proc_info(thd, "reset");
 	reset_thd(thd);
-	thd_proc_info(thd, "");
+	thd_proc_info(thd, proc_info);
 }