[3.1.2 and older] birdc doesn't output the possible command expansions list

Hello, I've observed an issue with `bird` 3.1.2 that is also reproducible in 2.17.1, but not with 2.15.1 (i. e. a regression somewhere between 2.15.1 and 2.17.1). After starting the `bird` service, on 2.17.1 and newer:

# birdc bird> show stat Ambiguous command, possible expansions are:

On 2.15.1, the output is correct:

# birdc bird> show stat Ambiguous command, possible expansions are: show status                                    Show router status show static [<name>]                           Show details of static protocol bird>

This was tested on ALT Linux (downstream issue: https://bugzilla.altlinux.org/54787). Per the maintainer, it's likely an issue in `bind` itself rather than the package, hence reporting here. Thanks!