Ie9 negative width sprite fix

In the Sprite class, it is possible to pass a 0 or negative value (or to have a 0 or negative value(s) result from calculation) for the width and height of the sprite.  IE9 (and possibly IE10) does not allow for a 0  or negative width when drawing on the CANVAS element.  Trying to do so results in a "DOM Exception: INDEX_SIZE_ERR (1)" error in the console.