Virtual listview with item renderers

[Shallowmallow]

Bug : for listviews with item renderers, only 6 item appear when it's virtual, all of them when it's not .

<listview id="lv2" width="200" height="150" selectedIndex="1"  virtual="true">
        <item-renderer layout="horizontal" width="100%">
            <checkbox id="complete" />
            <label width="100%" id="item" verticalAlign="center" />
            <image id="image" />
        </item-renderer>
        <data>
            <item complete="false" item="Item 1" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="true" item="Item 2" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="true" item="Item 3" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="false" item="Item 4" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="true" item="Item 5" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="true" item="Item 6" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="false" item="Item 7" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="true" item="Item 8" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="false" item="Item 9" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="false" item="Item 10" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="false" item="Item 11" image="haxeui-core/styles/default/haxeui_tiny.png" />
            <item complete="true" item="Item 12" image="haxeui-core/styles/default/haxeui_tiny.png" />
        </data>
    </listview>
    ```