Well, I did a thing that I normally would not - tried to unpack it directly to Kobo. And then I disconnected the Glo. My only excuse is that I wasn't expecting that it will try to update with a piece of firmware file. My bad...
I have a backup which is month old but in this time I read maybe only one or two books so you may say that database is quite recent.
So after adding books and processing I may restore the database?
A little update about restoring databse.
I tried to do this but after that Glo was behaving rather strange, not all read books were seen by it as read, not all were even seen by the device. I guess that recovering database is safe and simple only if you have a backup of it on the same firmware as your Glo is.