b2CreateCapsuleShape guards against a small/zero capsule length but b2Shape_SetCapsule does not.

[MelvMay-Unity]

As per the conversation here: https://discord.com/channels/460295137705197568/1250865746494619650/1431172850638786630

Also, I'm curious if using such as capsule when creating a shape proxy or via the mover is still fine or may cause problems.

It would seem for a shape proxy that maybe doing something similar and averaging center1/center2 as a single point + radius would be better?