patch 9.0.0394: Cygwin: multibyte characters may be broken in terminal window

Problem:    Cygwin: multibyte characters may be broken in terminal window.
Solution:   Adjust how to read and write on the channel. (Ken Takata,
            closes #11063)

Author: k-takata

src/channel.c

@@ -3589,6 +3589,24 @@ channel_free_all(void)
 // Buffer size for reading incoming messages.
 #define MAXMSGSIZE 4096
 
+/*
+ * Check if there are remaining data that should be written for "in_part".
+ */
+    static int
+is_channel_write_remaining(chanpart_T *in_part)
+{
+    buf_T *buf = in_part->ch_bufref.br_buf;
+
+    if (in_part->ch_writeque.wq_next != NULL)
+	return TRUE;
+    if (buf == NULL)
+	return FALSE;
+    return in_part->ch_buf_append
+	    ? (in_part->ch_buf_bot < buf->b_ml.ml_line_count)
+	    : (in_part->ch_buf_top <= in_part->ch_buf_bot
+			    && in_part->ch_buf_top <= buf->b_ml.ml_line_count);
+}
+
 #if defined(HAVE_SELECT)
 /*
  * Add write fds where we are waiting for writing to be possible.
@@ -3604,8 +3622,7 @@ channel_fill_wfds(int maxfd_arg, fd_set *wfds)
 	chanpart_T  *in_part = &ch->ch_part[PART_IN];
 
 	if (in_part->ch_fd != INVALID_FD
-		&& (in_part->ch_bufref.br_buf != NULL
-		    || in_part->ch_writeque.wq_next != NULL))
+		&& is_channel_write_remaining(in_part))
 	{
 	    FD_SET((int)in_part->ch_fd, wfds);
 	    if ((int)in_part->ch_fd >= maxfd)
@@ -3629,8 +3646,7 @@ channel_fill_poll_write(int nfd_in, struct pollfd *fds)
 	chanpart_T  *in_part = &ch->ch_part[PART_IN];
 
 	if (in_part->ch_fd != INVALID_FD
-		&& (in_part->ch_bufref.br_buf != NULL
-		    || in_part->ch_writeque.wq_next != NULL))
+		&& is_channel_write_remaining(in_part))
 	{
 	    in_part->ch_poll_idx = nfd;
 	    fds[nfd].fd = in_part->ch_fd;
@@ -3865,8 +3881,6 @@ channel_read(channel_T *channel, ch_part_T part, char *func)
 	// Store the read message in the queue.
 	channel_save(channel, part, buf, len, FALSE, "RECV ");
 	readlen += len;
-	if (len < MAXMSGSIZE)
-	    break;	// did read everything that's available
     }
 
     // Reading a disconnection (readlen == 0), or an error.

src/version.c

@@ -703,6 +703,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    394,
 /**/
     393,
 /**/