By default the SVG spinner should be display none at all times. Only
display block the SVG when the infinite scroll is in the loading state.
Closes#5776
Previously infinite scroll would only do checks when it got to
scrollTop it’s never seen before. However, this then requires a reset()
function if the underlying data changes, which would become an API
gotcha that would be a common source of problems for developers. Always
checking on scroll change should have little performance impact since
it was always checking while scrolling down anyway, it just wasn’t
checking when scrolling up. Now it always checks.
