patch 7.4.1789

Problem:    Cannot use ch_read() in the close callback.
Solution:   Do not discard the channel if there is readahead.  Do not discard
            readahead if there is a close callback.

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1789,
 /**/
     1788,
 /**/