fa91dd31 "5th step to remove tools/rtti.hxx" had
changed this from an exact-type check

  pObject->Type() == TYPE(SdrRectObj)

to a type-or-subtype-of check

  dynamic_cast< const SdrRectObj* >(pObject) != nullptr

but SdrRectObject is not a final class (SdrCaptionObj, SdrCircObj, ... derive
from it).

Change-Id: Ia820ee5475fbaf7a00ab0093d949c3cbd3406f83