Add support to handle KML with outline parameter set to 0

[ltkum]

• When trying to create a vectorSource from an OpenLayers layer with a KML source, if the outline parameter in the polystyle is set to 0, it currently crashes ( I offer a quick fix in the following PR : Support function in geometries: #40 ) as it tries to set a geometry as a function without any parameter.

• The issue continues further when we manage to set the geometries, as openlayers create two styles when the outline parameter from a KML source is set to 0, and thus the library creates two features that overlap each other, one with a outline, one without. This causes print jobs to have a wrong opacity and an outline when we want None.