citytile of cell class not initialized.

[SHJongsma]

The API documentation says for the cell:
citytile: CityTile - the citytile that is on this Cell. Equal to none or null equivalents in other languages if there is no CityTile here.

However, for the C++ implementation, citytile is not initialized to: nullptr. Therefore, it is actually uninitialized; at least that is what my valgrind says.