Fix an error in generating person metadata if there's no party
Fix an error in generating person metadata if there's no party

We have no party information for some people in the database, so avoid
an error if one of those people's pages is viewed.

DemocracyClub/yournextrepresentative,datamade/yournextmp-popit,openstate/yournextrepresentative,openstate/yournextrepresentative,neavouli/yournextrepresentative,mysociety/yournextmp-popit,mysociety/yournextmp-popit,datamade/yournextmp-popit,openstate/yournextrepresentative,DemocracyClub/yournextrepresentative,YoQuieroSaber/yournextrepresentative,DemocracyClub/yournextrepresentative,openstate/yournextrepresentative,YoQuieroSaber/yournextrepresentative,YoQuieroSaber/yournextrepresentative,mysociety/yournextrepresentative,datamade/yournextmp-popit,neavouli/yournextrepresentative,mysociety/yournextmp-popit,mysociety/yournextmp-popit,YoQuieroSaber/yournextrepresentative,datamade/yournextmp-popit,mysociety/yournextrepresentative,openstate/yournextrepresentative,YoQuieroSaber/yournextrepresentative,mysociety/yournextrepresentative,mysociety/yournextrepresentative,neavouli/yournextrepresentative,neavouli/yournextrepresentative,datamade/yournextmp-popit,mysociety/yournextmp-popit,neavouli/yournextrepresentative,mysociety/yournextrepresentative