fix #1477

transport/internet/kcp/io.go

@@ -26,6 +26,9 @@ type KCPPacketReader struct {
 
 func (r *KCPPacketReader) Read(b []byte) []Segment {
 	if r.Header != nil {
+		if int32(len(b)) <= r.Header.Size() {
+			return nil
+		}
 		b = b[r.Header.Size():]
 	}
 	if r.Security != nil {