Merged requested to merge fix/nan_obm_bdgs into master
GDEProcessor.process_group_data_unit_tiles() returned NaN number of OBM buildings when there were
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.