ext/com_dotnet: release the held IUnknown in com_get_active_object()

The cleanup block guarded on `unk` but released `obj`, so a successful
GetActiveObject() released the IDispatch proxy twice (once already under
the obj guard) and never released the IUnknown it returned, leaking it.
Release `unk` so each interface pointer is released exactly once.

Author: iliaal

ext/com_dotnet/com_com.c

@@ -321,7 +321,7 @@ PHP_FUNCTION(com_get_active_object)
 		IDispatch_Release(obj);
 	}
 	if (unk) {
-		IUnknown_Release(obj);
+		IUnknown_Release(unk);
 	}
 	efree(module);
 }