This commit fixes a minor bug in the ForEachChannel method of the
ChannelGraph struct. Rather than ErrGraphNoEdgesFound being returned if
either of the edge related buckets hadn’t been created yet,
ErrGraphNodesNotFound was being returned.
To fix this bug, we now properly return ErrGraphNoEdgesFound.
Additionally a mental note to roasbeef has been left as the current
code currently assumes that eventually both directions of the channel
edge will be advertised. However, this may not necessarily be the case
in a live network, since a side chooses to preferentially advertise a
channel or not.
42c90794ac