scour.py: minor rearrangement for the sake of clarity

Created by: mfwitten

There has been a minor rearrangement of the code that handles the children of the element being serialized: The relevant if statement has had its condition effectively negated and thus has also had its consequent and alternative swapped; now, there is a very short consequent, followed by a very long alternative, rather than a very long consequent followed by a very short alternative.