fix missing to reduce global big tx counter

It might cause job stuck.

Author: ffffwh

driver/mysql/extractor.go

@@ -1585,7 +1585,7 @@ func (e *Extractor) Shutdown() error {
 	e.shutdown = true
 	close(e.shutdownCh)
 
-	if e.binlogReader != nil && atomic.LoadInt32(&e.binlogReader.BigTxCount) > 1 {
+	if e.binlogReader != nil && atomic.LoadInt32(&e.binlogReader.BigTxCount) >= 1 {
 		g.SubBigTxJob()
 	}