vcard-manager.c: correct assertion about when priv->edits is NULL
vcard-manager.c: correct assertion about when priv->edits is NULL

It previously didn't take into account the fact that it could be non-NULL if
there was a SET request in progress.

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