Refuse to create a `DirectedChannelInfo` if either directional update is missing

As a followup to #1815 and #1735 we should extend #1815 to check for the presence of both directions, rather than only the requested direction, before constructing a `DirectedChannelInfo`. This avoids routing over channels that we consider removal candidates as of #1735.

@naumenkogs had already started work on this in #1735, so he may want to pick this up.