check for styles.opacity being undefined in qq.css

This corrects an issue we ran into using fineuploader basic with IE7 where, if you inspect the DOM element that is passed to fineuploader as `button` you can see that the element has inline style information something like: `filter: alpha(NaN)`. 

[This Stack Overflow thread](http://stackoverflow.com/a/15505748) suggested this fix and we implemented it and found it corrects the issue. @rnicholus suggested in that same thread to use a nested element, which we did not try. I'm of the opinion that if this affected us as well as the original asker (and it took us a good 30 minutes to discover what was going on) that it's worth correcting since the project states it supports IE7.