server: fix ComStmtSendLongData when data length is 0 (#7485)
server: fix ComStmtSendLongData when data length is 0 (#7485)



pingcap/tidb,ming-relax/tidb,pingcap/tidb,c4pt0r/tidb,Nify/tidb,cosmtrek/tidb,tiancaiamao/tidb,kyle-wang/tidb,ming-relax/tidb,c4pt0r/tidb,Nify/tidb,kyle-wang/tidb,qiuyesuifeng/tidb,pingcap/tidb,coocood/tidb,kyle-wang/tidb,tiancaiamao/tidb,Cofyc/tidb,c4pt0r/tidb,mccxj/tidb,ngaut/tidb,cosmtrek/tidb,XuHuaiyu/tidb,ngaut/tidb,XuHuaiyu/tidb,EvilMcJerkface/tidb,Cofyc/tidb,pingcap/tidb,c4pt0r/tidb,EvilMcJerkface/tidb,c4pt0r/tidb,ngaut/tidb,pingcap/tidb,c4pt0r/tidb,mccxj/tidb,coocood/tidb,pingcap/tidb,kyle-wang/tidb,qiuyesuifeng/tidb,wusphinx/tidb,ngaut/tidb,kyle-wang/tidb,kyle-wang/tidb,wusphinx/tidb,ngaut/tidb,ngaut/tidb