This fixes an issue while using to_wkt as a ufunc on an array with GEOS >= 3.9.0 with empty geometries. The issue (discovered with GH-2004) is that the WKT writer finishes sometimes too early while processing geometries.

For instance, using shapely 2.0.2 with GEOS 3.12.1 via conda-forge:

import shapely

empty_geoms = shapely.from_wkt(["POINT Z EMPTY", "POINT Z EMPTY"])
list(shapely.to_wkt(empty_geoms))
# ['POINT Z EMPTY', None]

It also seems that there could be a missing Py_XDECREF(*out);, but I'd appreciate someone with Python C API expertise to weight in.

This can be backported to maint-2.0 too.