Improve nonCoveredPoint checks

Improve nonCoveredPoint checks

- Skip trying to the right of a covering element if that's further to
  the right than the element's rect.

- If the covering element is a parent to the element we're checking,
  don't try looking to the right of the parent. It is _very_ unlikely
  that we'll find the element we're checking there. Instead, try the
  most likely point to be non-covered: The center of the element. This
  needs to be done because of pseudo-elements of the parent element
  which might cover the link partly, likely at the edges. Fixes #742.