Ensuring that $scope.onScroll gets defined scrollLeft- and scrollTop-values

Hi.

I sometimes got errors when the `$element.scroll`-binding had no proper object to get the `scrollTop`- and `scrollLeft`-properties from. That's when neither `e.detail` nor `e.originalEvent.deail` is defined. The previous solution basing on ternary operators didn't catch this option.

So I bloated the callback-function and added some "if-else-fugliness". What do you think?

Best regards
Emanuel