Don't rely on hasChanged() in ensureGeometries

It can be removed now because we now have a better caching
mechanism than before. It should therefore not be needed anymore.

Since nothing else calls hasChanged, we can finally get rid of it.
This simplifies the code and enables us to further improvements to the
code.

Change-Id: I51afe5a97311e3e361ae8b491ecbcd21bbedacd1
Reviewed-by: J-P Nurmi <jpnurmi@theqtcompany.com>