demo: updated TNullInterfacedObject implementation.
demo: updated TNullInterfacedObject implementation.

- It was missing the IUnknown declaration in the class
- The IUnknown signature has changed in recent FPC versions.

wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI