Fix #77177: Serializing or unserializing COM objects crashes

Fix #77177: Serializing or unserializing COM objects crashes

Firstly, we avoid returning NULL from the get_property handler, but
instead return an empty HashTable, which already prevents the crashes.
Secondly, since (de-)serialization obviously makes no sense for COM,
DOTNET and VARIANT objects (at least with the current implementation),
we prohibit it right away.