Avoid scrolling of lists and menus when navigating with cursor keys (#1489929)

program/js/app.js

@@ -1677,7 +1677,7 @@ function rcube_webmail()
       case 63232: // "up", in safari keypress
       case 63233: // "down", in safari keypress
         focus_menu_item(keyCode == 38 || keyCode == 63232 ? -1 : 1);
-        break;
+        return rcube_event.cancel(e);
 
       case 9:   // tab
         if (this.focused_menu) {

program/js/treelist.js

@@ -739,7 +739,7 @@ function rcube_treelist_widget(node, p)
         if (li.length) {
           focus_next(li, (mod = keyCode == 38 || keyCode == 63232 ? -1 : 1));
         }
-        break;
+        return rcube_event.cancel(e);
 
       case 37: // Left arrow key
       case 39: // Right arrow key