man gives wrong information in case of undocumented

[Alexis]

When trying to access an undocumented help, the help proposes to use "man 7 undocumented". Yet this page does not exist on my machine. Base installation of Ubuntu 18.04.

```
alexis@Oreo:~$ man 2 printf
No manual entry for printf in section 2
See 'man 7 undocumented' for help when manual pages are not available.
alexis@Oreo:~$ man 7 undocumented
No manual entry for undocumented in section 7
```

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: manpages 4.15-1
ProcVersionSignature: Ubuntu 5.3.0-26.28~18.04.1-generic 5.3.13
Uname: Linux 5.3.0-26-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.9
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Tue Jan 21 15:59:19 2020
Dependencies:

InstallationDate: Installed on 2019-08-22 (152 days ago)
InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
PackageArchitecture: all
SourcePackage: manpages
UpgradeStatus: No upgrade log present (probably fresh install)

[Sebastien Bacher (seb128)]

Thank you for your bug report, that seems to not be happening in the current Ubuntu serie, maybe it has been resolved in an update