Fix: b2CollideSegmentAndCapsule should pass manifold parameter to b2CollideCapsules

[mikuso]

This PR fixes the b2CollideSegmentAndCapsule function.

Explanation:

It seems to me that b2CollideCapsules was changed from the original in that it performs an in-place modification of the manifold parameter, rather than creating & returning a new one. (I assume this is for performance reasons?)

However, it looks like b2CollideSegmentAndCapsule, a function which was also modified from the original (seemingly with the same intent), does not correctly pass the manifold parameter through to the b2CollideCapsules function it depends upon.

This fixes that.

Additionally:

This also corrects an erroneous call to manifold.clear() with a parameter (0) which is seemingly inert and unnecessary, as this function does not accept any parameters.