Maraxsis + Krastorio 2 Compatibility Fix

This is a small compatibility fix for using Maraxsis together with Krastorio 2 or Krastorio2 Spaced Out.

What it fixes

Without this fix, the game may fail during startup with an error similar to:

```text
maraxsis/compat/krastorio-2.lua:132:
attempt to index field 'effect_receiver' (a nil value)