patch 9.0.0311: test for hit-Enter prompt fails

Problem:    Test for hit-Enter prompt fails.
Solution:   Only reset cmdline_row when 'cmdheight' is zero.

src/drawscreen.c

@@ -831,8 +831,9 @@ after_updating_screen(int may_resize_shell UNUSED)
     handle_any_postponed_drop();
 #endif
 
+    if (p_ch == 0)
 	// in case it was changed in dont_use_message_window()
-    cmdline_row = Rows - p_ch;
+	cmdline_row = Rows;
 }
 
 /*

src/version.c

@@ -707,6 +707,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    311,
 /**/
     310,
 /**/