Fix bbox density about bboxify-labels

[kapadia]

@ansis I adjusted the number of bounding boxes that are created for each segment of the polyline.

Previously an extra box was created that would encroach on the next segment. This was done to ensure the very last segment included the final box that covered the entire label length.

Now a last box is only added on the last segment of the polyline, making the boxes look more regular.

before (left) after (right)