This fixes the situation where you start the receiver first, then start
the sender, then you hit TAB on the receiver.
This somewhat improves the situation where you start the receiver first,
hit TAB (getting nothing), then start the sender, then hit TAB on the
receiver again. The second TAB will list the channel-ids, but won't
insert the only one as it's supposed to. You must type something (which
you can erase) and then hit TAB again to get a unique channel-id
inserted. But at least you can tell which one to type.
The first TAB runs the completer with readline.get_completion_type()
equal to 9=TAB=try-to-insert. The second (and subsequent) TABs use
63=?=list-matches, and it won't go back to 9 until you type something.
12414fd8be