Check tidal samples are not always 0 when identifying an NSBH system
The purpose of this MR is to refine the _check_for_NSBH_system
function in the pesummary.gw.conversions._Conversion
class to check if all tidal samples are zero. If they are, we can treat this as a BBH system. This fixes an issue identified by @aditya.vijaykumar (see PESummary-help channel on mattermost for details).