Added some guards to prevent clumping to non existing particles. Also, adjusted threaded child path evaluation, so each child is evaluated once - previously virtual parents were done twice.
to prevent double-freeing/invalid mem access.
This can happen with the "virtual parents" feature, which generates both
parent and child paths. Each task free function also freed the shared
context, leading to double freeing.
easier.
This code is badly broken and needs to be replaced, but at least having
a workable code structure might help with quick hacks to fix the worst
cases.
