search-channel: stop using lm_message_node_get_child_with_namespace
search-channel: stop using lm_message_node_get_child_with_namespace

In all cases, we wanted a direct child.

mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble