Fixes #3496. Escape Key not invoking OnKeyDown on Unix.

Terminal.Gui/ConsoleDrivers/CursesDriver/CursesDriver.cs

@@ -505,6 +505,7 @@ namespace Terminal.Gui {
 					keyHandler (key);
 				} else {
 					k = Key.Esc;
+					keyDownHandler (new KeyEvent (k, MapKeyModifiers (k)));
 					keyHandler (new KeyEvent (k, MapKeyModifiers (k)));
 				}
 			} else if (wch == Curses.KeyTab) {