Fix warning in the JavaScript code when trying to access a method of a null object.

The method jq() always returns an array, so we have to check the length of the
array to know  when the search is empty.

FEA: ItEr75S04BugFixing

ganttzk/src/main/resources/web/js/ganttz/TaskComponent.js

@@ -191,7 +191,7 @@ ganttz.TaskComponent = zk.$extends(zul.Widget, {
         this.mouseOverTask = true;
         this._tooltipTimeout = setTimeout(jq.proxy(function(offset) {
             var element = jq("#tasktooltip" + this.uuid);
-            if (element!=null) {
+            if (element.length > 0) {
                 element.show();
                 offset = ganttz.GanttPanel.getInstance().getXMouse()
                         - element.parent().offset().left