SCI: Allow invalid references to kUnload() - bug #6600

Since the reference will be invalidated anyway by kUnload itself,
there's no real reason to check for its validity. We do the same with
kGraph() and kDisplay().
SCI: Show the address segment when trying to free hunks from an invalid
address
SCI: Add the French version of Phantasmagoria - bug #6574
SCI: Extend hack to fix regression in GK1