patch 8.0.1000: cannot open a terminal without running a job in it

Problem:    Cannot open a terminal without running a job in it.
Solution:   Make ":terminal NONE" open a terminal with a pty.
diff --git a/src/channel.c b/src/channel.c
index 1680d0d..b31d95d 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -503,6 +503,10 @@
     if (!CH_HAS_GUI)
 	return;
 
+    /* gets stuck in handling events for a not connected channel */
+    if (channel->ch_keep_open)
+	return;
+
 # ifdef FEAT_GUI_X11
     /* Tell notifier we are interested in being called
      * when there is input on the editor connection socket. */
@@ -548,9 +552,12 @@
 {
     if (channel->CH_SOCK_FD != INVALID_FD)
 	channel_gui_register_one(channel, PART_SOCK);
-    if (channel->CH_OUT_FD != INVALID_FD)
+    if (channel->CH_OUT_FD != INVALID_FD
+	    && channel->CH_OUT_FD != channel->CH_SOCK_FD)
 	channel_gui_register_one(channel, PART_OUT);
-    if (channel->CH_ERR_FD != INVALID_FD)
+    if (channel->CH_ERR_FD != INVALID_FD
+	    && channel->CH_ERR_FD != channel->CH_SOCK_FD
+	    && channel->CH_ERR_FD != channel->CH_OUT_FD)
 	channel_gui_register_one(channel, PART_ERR);
 }
 
@@ -3247,11 +3254,13 @@
 
     /* Reading a disconnection (readlen == 0), or an error. */
     if (readlen <= 0)
-	ch_close_part_on_error(channel, part, (len < 0), func);
-
+    {
+	if (!channel->ch_keep_open)
+	    ch_close_part_on_error(channel, part, (len < 0), func);
+    }
 #if defined(CH_HAS_GUI) && defined(FEAT_GUI_GTK)
-    /* signal the main loop that there is something to read */
-    if (CH_HAS_GUI && gtk_main_level() > 0)
+    else if (CH_HAS_GUI && gtk_main_level() > 0)
+	/* signal the main loop that there is something to read */
 	gtk_main_quit();
 #endif
 }
@@ -3509,13 +3518,14 @@
 }
 # endif
 
-# if defined(WIN32) || defined(PROTO)
+# if defined(WIN32) || defined(FEAT_GUI) || defined(PROTO)
 /*
  * Check the channels for anything that is ready to be read.
  * The data is put in the read queue.
+ * if "only_keep_open" is TRUE only check channels where ch_keep_open is set.
  */
     void
-channel_handle_events(void)
+channel_handle_events(int only_keep_open)
 {
     channel_T	*channel;
     ch_part_T	part;
@@ -3523,6 +3533,9 @@
 
     for (channel = first_channel; channel != NULL; channel = channel->ch_next)
     {
+	if (only_keep_open && !channel->ch_keep_open)
+	    continue;
+
 	/* check the socket and pipes */
 	for (part = PART_SOCK; part < PART_IN; ++part)
 	{