Don't fill wxListEvent::m_item when using virtual list control in wxMSW.

Don't fill wxListEvent::m_item when using virtual list control in wxMSW.

When using virtual list control the main program already has the items data so
it's completely useless to call GetItem() when preparing an event for it. It
is also inefficient to call GetItem() for potentially many items.

For both of these reasons the generic version already didn't fill the item
contents for virtual list controls events. Now modify wxMSW to not do it
neither.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70271 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775