lib-navigation MDL-21113 Fixed minor javascript error when positioning sidepanel tabs for display

lib/javascript-navigation.js

@@ -609,7 +609,7 @@ navigation_tab_panel.prototype.resize_tab = function () {
 
     // This makes sure that if the panel is big it is moved up to ensure we don't
     // have wasted space above the panel
-    if ((tabtop+tabheight)>screenheight && tabtop > 10) {
+    if ((tabtop+tabheight)>(screenheight+scrolltop) && tabtop > 10) {
         tabtop = (screenheight-tabheight-10);
         if (tabtop<10) {
             tabtop = 10;