executor: fix threshold check without group by bug (#14961)
executor: fix threshold check without group by bug (#14961)

Signed-off-by: crazycs <174f850cd6ed76c2653f481397d398dd570f1f87@gmail.com>
pingcap/tidb,kyle-wang/tidb,coocood/tidb,XuHuaiyu/tidb,XuHuaiyu/tidb,coocood/tidb,ngaut/tidb,kyle-wang/tidb,c4pt0r/tidb,ngaut/tidb,ngaut/tidb,pingcap/tidb,kyle-wang/tidb,ngaut/tidb,c4pt0r/tidb,c4pt0r/tidb,pingcap/tidb,c4pt0r/tidb,kyle-wang/tidb,pingcap/tidb,EvilMcJerkface/tidb,ngaut/tidb,c4pt0r/tidb,Cofyc/tidb,c4pt0r/tidb,pingcap/tidb,Cofyc/tidb,ngaut/tidb,kyle-wang/tidb,kyle-wang/tidb,EvilMcJerkface/tidb,pingcap/tidb