Effect.SlideDown, Effect.SlideUp: oldInnerBottom = "NaNpx" in Opera

[victor-homyakov]

Opera 10/Linux shows javascript errors after executing SlideUp/SlideDown effects in code
... setStyle({bottom: oldInnerBottom})
because
var oldInnerBottom = element.down().getStyle('bottom')
will give result "NaNpx". There must be additional check, e.g.
var oldInnerBottom = element.down().getStyle('bottom');
if (oldInnerBottom == "NaNpx") {
oldInnerBottom = "";
}