Use NSBH fits when all lambda_1 samples = 0
The purpose of this MR is to extend the pesummary.gw.conversions._check_for_NSBH_system function to pass when all lambda_1 samples are exactly equal to 0 (implying the BH limit).
The purpose of this MR is to extend the pesummary.gw.conversions._check_for_NSBH_system function to pass when all lambda_1 samples are exactly equal to 0 (implying the BH limit).