[FCLayout] ILayoutElement.getMinBoundsWidth() doesn't return the correct measured width if item has explicit width and height.

Steps to reproduce:
1. Compile and run the following app

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark">

<fx:Script>
<![CDATA[
protected function button1_clickHandler(event:MouseEvent):void

{ result.text = button1.getMinBoundsWidth(false) + "," + button2.getMinBoundsWidth(false) + "," + button3.getMinBoundsWidth(false) + "," + button4.getMinBoundsWidth(false); }

]]
>
</fx:Script>

<s:Button id="button1" x="100" y="100"/>
<s:Button id="button2" x="100" y="200" width="50"/>
<s:Button id="button3" x="100" y="300" height="50"/>
<s:Button id="button4" x="100" y="400" width="50" height="50"/>

<s:Button x="390" y="49" label="getMinBoundsWidth" click="button1_clickHandler(event)"/>
<s:TextArea id="result" x="383" y="112" width="242" height="197"/>
</s:Application>

2. Click the button labelled "getMinBoundsWidth"

Actual Results: getMinBoundsWidth() returns 21 for button1, button2, and button3, but returns 0 for button4.

Expected Results:getMinBoundsWidth() returns the same value for all 4 buttons

This bug affects Catalyst, which uses getMinBoundsWidth() when resizing objects, or when applying/removing constraints. This is the cause of bug TH-11616.