Fix issue with line height calculation when using older versions of jQuery

jquery.mousewheel.js

@@ -58,7 +58,11 @@
         },
 
         getLineHeight: function(elem) {
-            return parseInt($(elem)['offsetParent' in $.fn ? 'offsetParent' : 'parent']().css('fontSize'), 10);
+            var $parent = $(elem)['offsetParent' in $.fn ? 'offsetParent' : 'parent']();
+            if (!$parent.length) {
+                $parent = $('body');
+            }
+            return parseInt($parent.css('fontSize'), 10);
         },
 
         getPageHeight: function(elem) {

test/index.html

@@ -113,7 +113,7 @@
                 $('#jqueryVersion').html($.fn.jquery);
 
                 var loghandle = function(event, delta) {
-                    var o = '', id = event.currentTarget.id;
+                    var o = '', id = event.currentTarget.id || event.currentTarget.nodeName;
 
                     o = '#' + id + ':';
 
@@ -137,6 +137,11 @@
                     log( o );
                 };
 
+                $(document)
+                    .mousewheel(function(event, delta) {
+                        loghandle(event, delta);
+                    });
+
                 $('#test1')
                     .mousewheel(function(event, delta) {
                         loghandle(event, delta);