Option --version displays UNKNOWN

One would expect to see rygel's version when calling it with the --version option. Instead "UNKNOWN" is displayed

```
# rygel --version
Rygel UNKNOWN
```
--------------

# lsb_release -rd
Description: Ubuntu 19.10
Release: 19.10

# apt-cache policy rygel
rygel:
  Installed: 0.38.1-2ubuntu3.3
  Candidate: 0.38.1-2ubuntu3.3
  Version table:
 *** 0.38.1-2ubuntu3.3 500
        500 http://ro-mirrors.evowise.com/ubuntu eoan-updates/main amd64 Packages
        500 http://ro-mirrors.evowise.com/ubuntu eoan-security/main amd64 Packages
        100 /var/lib/dpkg/status
     0.38.1-2ubuntu3 500
        500 http://ro-mirrors.evowise.com/ubuntu eoan/main amd64 Packages