Fixed NaN OBM buildings in GDEProcessor.process_group_data_unit_tiles()
GDEProcessor.process_group_data_unit_tiles()
returned NaN number of OBM buildings when there were quadkeys
in data_unit_tiles
that were not in obm_buildings_per_quadkey
. If a quadkey is not in obm_buildings_per_quadkey
it means that no OBM buildings with that quadkey were found in the data unit. Thus, those NaNs should be zeroes.