QDeclarativeGeoMapItemBase::childMouseEventFilter: Do not eat release events

The filter can lead to events outside of the item being "dismissed" or
rather sent the the map item.  When testing with MapRects, when dragging
a map rect fast, I would sometimes get release events outside of the map
rect, which would then end up being deliverd to the
QDeclarativeGeopMapItemBase subclass. This effectively prevents
MouseAreas inside of the GeoMapItem from receiving their release event.
That in turn breaks follow up events to said items.

While I still consider this extremely evil and bad behavior, at least
this doesn't completely break event delivery any more.

Change-Id: I228d64e04140e2434779d07d8f03a8e9f2d11f83
Reviewed-by: Paolo Angelelli <paolo.angelelli@qt.io>