OO-709: fix javascript error if the table of items isn't rendered

src/main/java/org/olat/modules/qpool/ui/_content/items.html

@@ -27,7 +27,8 @@ jQuery(function() {
 	var footerHeight = jQuery('#b_footer').height() + jQuery('#qbuttons').height();
 	var maxHeight = winHeight - headerHeight - footerHeight - 50;
 	## padding arount table = relative position of table (space for search field) + height of action buttons below table + some extra space
-	var panePadding = jQuery('.dataTables_wrapper').position().top + jQuery('.o_qpool_button_bar_box').height() + 80;
+	var dataTablesPos = jQuery('.dataTables_wrapper').position()
+	var panePadding = (dataTablesPos ? dataTablesPos.top : 0) + jQuery('.o_qpool_button_bar_box').height() + 80;
 
 	jQuery('#qpoolcontainer').width(width).height(maxHeight).layout({
 		north: { size: '50%' },