cgtop: make sure help text doesn't cause main contents to move

Let's always keep space for the full help text. (We used to do that, but
recently another line of help was added which broke this.)

src/cgtop/cgtop.c

@@ -602,7 +602,7 @@ static void display(Hashmap *a) {
                 _cleanup_free_ char *ellipsized = NULL;
                 const char *path;
 
-                if (on_tty() && j + 5 > rows)
+                if (on_tty() && j + 6 > rows)
                         break;
 
                 g = array[j];