fix bug where images loaded from chrome cache results in 0 WIDTH elements

[BrunoRB]

In some chrome versions (linux 54.0 being one of them) sometimes the getComputedStyle(data.target[0]).width call in Spin.setLayout returns the value auto which makes the image width value 0 ( w = Number(style.width.replace('px', ''))|0; === 0), thus making it invisible. It usually happens when spritesbin fully loaded the images, then you change to another page and then you go back to the previous page using the browser back button. My best guess is that chrome triggers the img.onload event for cached images without (or before) computing the image dimensions.