qgis/QGIS — pull request #1149 by p0cisk (2014-02-08 11:11:47+00:00)
Title: [processing]Fix "float division by zero" in polygonize algorithm if no

polygons were created.
For shapely 1.2.16+ and GEOS 3.2+ unary_union will be used for noding
lines - union method sometimes failed to create properly noded polyline.