Combining relative layout and percentage based layout produces wrong results on windows

When layouting a widget B relative to another widget A, which has a percentage based layout, widget B will be positioned offscreen.

```js
const {Composite, ui} = require('tabris');

new Composite({
left: 0, top: 0, bottom: 0, right: '50%',
background: 'red'
}).appendTo(ui.contentView);

new Composite({
left: ['prev()', 0], top: 0, bottom: 0, right: 0,
background: 'blue'
}).appendTo(ui.contentView);

```