src/presence-cache.c: Fix avatar conflict with several resources (Bug fd.o #23684)
src/presence-cache.c: Fix avatar conflict with several resources (Bug fd.o #23684)

community-ssu/telepathy-gabble,mlundblad/telepathy-gabble,jku/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,community-ssu/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble