fix highlight when using animate

[gboros]

when animate is used, the dropdown is not scrolled to the selected item - this commit calls "_ensureHighlightVisible" in this case, to fix it

[Jefiozie]

HI @gboros can you show a working an non working example for me?
So I can see what the original problem is ,thanks

[gboros]

hi
here is a non-working example : https://plnkr.co/edit/TWDf59jpdY7UuFf3BtTI?p=preview The dropdown should scroll to 'eleven'. If you change to use the 'select-fixed.js', that contains the PR, it will scroll

[Jefiozie]

Could you make a test for this? So that future adjustments won’t break.