Sprite Canvas Render: Add texture loaded check before drawing

I've run into an inconsistency between the WebGL rendering and canvas rendering where the canvas render for a sprite would throw an InvalidStateError when attempting to draw a sprite before the texture has loaded (or if the texture failed to load due to missing image file).  Adding a check before drawing to ensure the texture is loaded prevents this error from being thrown.

It appears the cause of this exception is related to passing in a 0 width image context.drawImage, see http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2013-September/040873.html for some discussion on this issue.

This error is occurring on Chrome 32.0.1700.107

Let me know if you need any more info on this!