Change QDeclarativeGeoMapItemBase::map_ into a QPointer

Or else it may cause crashes on shutdown due to map_ not being parented
with QDeclarativeGeoMap and potentially being deleted earlier.

Change-Id: I2bed1c884eb556e48261371e889aae5e190476bc
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

src/location/declarativemaps/qdeclarativegeomapitembase_p.h

@@ -116,7 +116,7 @@ private Q_SLOTS:
     void baseCameraDataChanged(const QGeoCameraData &camera);
 
 private:
-    QGeoMap *map_;
+    QPointer<QGeoMap> map_;
     QDeclarativeGeoMap *quickMap_;
 
     QSizeF lastSize_;