Comment 6 for bug 1659256

@Eduard - Yes it's still present with the latest trunk revisions.

As for the check, I'm not sure we really need it indeed. If we remove it, we can keep w = h = 0 for the minimal size option.
For the record, it was added rev.2059 (http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/2059). The previous revisions tested with -1.