Seed-based painting fails to paint within margin.

[Juan Pablo Caram]

The seedpoint is taken from the original polygon:

seedpoint = polygon.representative_point()

But then the buffered seed is intersected with the path_margin:

path = path.intersection(path_margin)

which can result in an empty geometry instantly if the seedpoint is between the polygon and the the path_margin.

[Juan Pablo Caram]

Solved in commit fd2657a.