An explicit std::move would be needed in the return statements, as there's a
conversion from VclPtrInstance to base class VclPtr involved.  One more reason
to better get rid of VclPtrInstance completely in favor of VclPtr::Create, as
already mentioned in
<https://lists.freedesktop.org/archives/libreoffice/2017-May/077756.html>
"VclPtr some improvements ?"

Change-Id: Id96a58b425749b9be07b422bb4161a3af864ff6c