Bridge angle partial fix

Here is ugly fix for clipper problem - removing endpoint from end of polyline.
And a fix for bridge angle detection.
There is still room for improvement:
- angle detection could search around best coarse candidates
- bridge with short lines should be preferred (maybe i't enough to use `sum(map $_->length ** .9, @clipped_lines) // 0;` as metric)
- angle detection with short line preference could be applied to bridges with closed boundary