Coverflow slider safari bug

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@lukeed
I have a coverflow slider with 9 slides and the following settings

```
glSlider = new Bee3D(coversSlider, {
effect: 'coverflow',
focus : 4,
navigation : {
enabled : true
},
listeners: {
keys: true,
touches: true,
clicks: true,
drag: true
},
autoplay : {
enabled : true,
pauseHover : true,
speed : 5000
},
loop : {
enabled : true,
continuous : true,
offset : 3
}
});
```

Whenever the last slide on the left (or right) has to loop around and go behind the other slides to land on the opposite side, it can be seen for a split second through the center of the slider.

I only see this bug on safari, desktop and mobile.

Any ideas on a possible fix for it?

Thanks!

Reproduce the Bee3D coverflow configuration in Safari on desktop and mobile, focusing on the last slide looping from one side to the other. Inspect the loop transition and verify that the slide is never visible through the slider center when the fix is complete.

Written by the indexing model from the issue text.