Correct 0-length path segmentization numpy fallback

This is as rare as it sounds. If you attempted to segment a path like M0,0zM1,1z with the npoint() code it would fail. There's a rare fallback when total length equals zero (and there exists segments). But, this was not properly fixed for use with numpy.

What's Changed

• npoint() zero length fallback by @tatarize in #191

Full Changelog: 1.7.4...1.7.5