Set URLLoader.data to the HTTP response text even when there is an IO_ERROR.

This is the behavior in Flash. Example:

var urlLoader:URLLoader = new URLLoader();
urlLoader.addEventListener(IOErrorEvent.IO_ERROR, function(event:IOErrorEvent):void
{
        // Will print either an empty String when run locally or the 404 HTML String when run on the web
        // If urlLoader.dataFormat is set to BINARY, then data will be a ByteArray object.
	trace(urlLoader.data);
});
urlLoader.load(new URLRequest("non-existent-openfl.txt"));