Enforce minimum sample interval for resampling.

The minimum sample interval is somewhat arbitrarily set to 16 × δ, where
δ is the Douglas–Peucker threshold.  This fixes cases where resampling
stops too early due to the perpendicular distance being below the
threshold; particularly for points that are far apart and whose
great-circle arc is projected to an S-shape.  The midpoint lies along a
straight line, failing the Douglas–Peucker check, but further resampling
produces an S-shape.

Ideally, resampling should also detect cases where an intermediate point
does not need to be drawn, i.e. where there truly is a straight line.
This fix causes points to be drawn at the minimum sample interval, and
thus may degrade performance slightly due to drawing redundant points.

Fixes
Avoid drawing redundant points when resampling.