Blender Git Loki

Cycles: Fix two small memory leaks and deduplicate table freeing

This commit makes remove_table skip the freeing if the offset is
already set to invalid - or, if it wasn't, set it to invalid after freeing.

That's what the current code was already doing in the Manager classes,
this change allows them to just call remove without the additional code.

Also, two potential memory leaks where new tables were always allocated
without freeing the old ones are fixed.

Reviewers: sergey, dingto, brecht

Differential Revision: https://developer.blender.org/D1974