Bug#672230: apt-listchanges: KeyError when only configuring packages

tags 672230 + patch
thanks

Hi!

I saw the same situation where apt had bombed out leaving packages unpacked 
but not configured. (I filled / ... oops.) I figured this was an opportunity to 
understand and fix this bug:

# apt-get -f install
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following extra packages will be installed:
  mysql-server-5.5
Suggested packages:
  tinyca
The following packages will be upgraded:
  mysql-server-5.5
1 upgraded, 0 newly installed, 0 to remove and 42 not upgraded.
2 not fully installed or removed.
Need to get 0 B/8,818 kB of archives.
After this operation, 481 kB disk space will be freed.
Do you want to continue [Y/n]?
Traceback (most recent call last):
  File "/usr/bin/apt-listchanges", line 238, in <module>
    main()
  File "/usr/bin/apt-listchanges", line 48, in main
    debs = apt_listchanges.read_apt_pipeline(config)