Divide by zero in convert.py

[MAD-OVERLORD]

As i already wrote you in a mail almost a month ago, most of my renderings(with estimator_radius="0") were ignored because of a divide by zero in genome/convert.py @ somewhere around line 147 after the division of course, what i somehow managed to cheap hack patch with ('filters.de.minimum', lambda d: (float(d['estimator_minimum']) / (float(d.get('estimator_radius', 11))+0.001)) if 'estimator_minimum' in d else None), but since i have a severe python phobia, it would be nice if you could implement a proper divide by zero protection.