Two gnome-system-log fixes

[Cosimo Cecchi <cosimoc gnome org>]

Hi,

I would like to merge these two gnome-system-log patches from Matthias
for 3.4:

https://bugzilla.gnome.org/show_bug.cgi?id=672513
- I think this is a regression from the GConf->GSettings migration. When
there's no log files list saved in preferences, GConf used to return
NULL, whereas GSettings returns an empty zero-terminated array

https://bugzilla.gnome.org/show_bug.cgi?id=672514
- fixes an obvious memory allocation bug that might cause a crash at
startup

Thanks for considering,
Cosimo