patch 9.0.0310: output of :messages dissappears when cmdheight is zero

Problem:    Output of :messages dissappears when cmdheight is zero.
Solution:   Do not use the messages window for :messages.  Make Esc close the
            messages window.
diff --git a/src/message.c b/src/message.c
index 096f274..e4f8af1 100644
--- a/src/message.c
+++ b/src/message.c
@@ -1077,6 +1077,7 @@
     }
 
     msg_hist_off = TRUE;
+    dont_use_message_window();
 
     p = first_msg_hist;
     if (eap->addr_count != 0)