After Texture has loaded, cannot use width/height properties

[kamranayub]

Reproduce:

/// <reference path="../../../../dist/Excalibur.d.ts"/>

var game = new ex.Engine(800, 503, "game");
var padTexture = new ex.Texture("gamepad.png");

game.start(new ex.Loader([padTexture])).then(start);

function start() {
   // Load gamepad sprite
   // BUG: Can't use padTexture.width/padTexture.height
   var padSprite = new ex.Sprite(padTexture, 0, 0, 800, 503);

   // Enable Gamepad support
   game.input.gamepads.enabled = true;

   // Draw gamepad
   var gamepad = new ex.Actor(0, 0, padSprite.width, padSprite.height);
   gamepad.addDrawing("bg", padSprite);
   game.add(gamepad);
}