patch 8.0.0964: channel write buffer does not work with poll()

Problem:    Channel write buffer does not work with poll().
Solution:   Use the same mechanism as with select().

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    964,
 /**/
     963,
 /**/