patch 7.4.2298

Problem:    It is not possible to close the "in" part of a channel.
Solution:   Add ch_close_in().

src/channel.c

@@ -2735,6 +2735,15 @@ channel_close(channel_T *channel, int invoke_close_cb)
     channel->ch_nb_close_cb = NULL;
 }
 
+/*
+ * Close the "in" part channel "channel".
+ */
+    void
+channel_close_in(channel_T *channel)
+{
+    may_close_part(&channel->CH_IN_FD);
+}
+
 /*
  * Clear the read buffer on "channel"/"part".
  */