Deal with edge case of zero length paths.

[RadostW]

When cropping larger OSM datasets sometimes paths with zero nodes are formed. Such paths break path -> svg code.

Checking for len < 2 resolves this problem.

[enzet]

Checks had failed mostly because of style issues. The project uses Black style formatter. To apply Black style, one have to simply run

black -l 80 map_machine

with the Black installed (pip install black).