Fix one definition rule violation in ncurses_ui.hh

The memory domain of Vector<DisplayBuffer> was different depending
on if display_buffer.hh has been included or not.

src/ncurses_ui.hh

@@ -96,7 +96,7 @@ private:
 
     struct Menu : Window
     {
-        Vector<DisplayLine> items;
+        Vector<DisplayLine, MemoryDomain::Display> items;
         Face fg;
         Face bg;
         DisplayCoord anchor;