Do not deliver hover events when item is not visible

Do not deliver hover events when item is not visible

This patch change the code to also skip invisible items (it was
done for disabled already) when deciding whether or not deliver the
hover events to an item. The rationale here is to follow the same
rule as the other mouse events.

Change-Id: If0fe6d64d1f7cfb8679ce11edda7c02dc3783f9b
Reviewed-on: http://codereview.qt.nokia.com/3861
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Alan Alpert <alan.alpert@nokia.com>