ddl: Handle the error of `ErrClientConnClosing` (#4117)
ddl: Handle the error of `ErrClientConnClosing` (#4117)


qiuyesuifeng/tidb,mccxj/tidb,ngaut/tidb,ngaut/tidb,XuHuaiyu/tidb,gaocegege/tidb,gaocegege/tidb,kyle-wang/tidb,EvilMcJerkface/tidb,kyle-wang/tidb,yangwenmai/tidb,pingcap/tidb,c4pt0r/tidb,qiuyesuifeng/tidb,c4pt0r/tidb,spongedu/tidb,8cbx/tidb,wusphinx/tidb,Nify/tidb,cosmtrek/tidb,kyle-wang/tidb,louishust/tidb,pingcap/tidb,yuanwhy/tidb,Cofyc/tidb,coocood/tidb,kyle-wang/tidb,pingcap/tidb,zimulala/tidb,kyle-wang/tidb,XuHuaiyu/tidb,c4pt0r/tidb,tiancaiamao/tidb,ming-relax/tidb,ngaut/tidb,kyle-wang/tidb,c4pt0r/tidb,mccxj/tidb,pingcap/tidb,cosmtrek/tidb,CodeRushing/tidb,pingcap/tidb,ming-relax/tidb,Cofyc/tidb,zimulala/tidb,louishust/tidb,8cbx/tidb,tiancaiamao/tidb,CodeRushing/tidb,pingcap/tidb,coocood/tidb,spongedu/tidb,Nify/tidb,wusphinx/tidb,ngaut/tidb,ngaut/tidb,EvilMcJerkface/tidb,yangwenmai/tidb,c4pt0r/tidb,yuanwhy/tidb,c4pt0r/tidb,ngaut/tidb