Fix SyscallVectorisedPacketWriter on windows

Author: nekohasekai

common/bufio/vectorised_windows.go

@@ -54,9 +54,13 @@ func (w *SyscallVectorisedPacketWriter) WriteVectorisedPacket(buffers []*buf.Buf
 	var innerErr error
 	err := w.rawConn.Write(func(fd uintptr) (done bool) {
 		name, nameLen := ToSockaddr(destination.AddrPort())
+		var bufs *windows.WSABuf
+		if len(iovecList) > 0 {
+			bufs = &iovecList[0]
+		}
 		innerErr = windows.WSASendTo(
 			windows.Handle(fd),
-			&iovecList[0],
+			bufs,
 			uint32(len(iovecList)),
 			&n,
 			0,