I think the problem is that we try to decode the alpha tag
even when it is not present, i.e., when _numlen is zero.
In fact, this has already been fixed in my current working
tree in a bit different way. Mostly due to the fact that I added a new
g_isi_sb_iter_get_struct() method, which allows a little
easier access to sub-blocks like the one above.
If you're curious, here's the tree with the fix:
http://meego.gitorious.org/~akiniemi/meego-cellular/ofono-aki/