Allow NULL and worldspawn to be used as entities
Allow NULL and worldspawn to be used as entities

Currently, the typecheck for entities in E2 says that invalid entities such as NULL and worldspawn aren't entities at all. This means that they're skipped inconsistently in places.

Fixes #1388. Fixes #1350.
garrysmodlua/wire,NezzKryptic/Wire,bigdogmat/wire,sammyt291/wire,dvdvideo1234/wire,thegrb93/wire,wiremod/wire,Grocel/wire