Fixes runtime with yellow slime extracts.

Undefined variable /datum/reagents/var/luminosity
proc name: on reaction (/datum/chemical_reaction/slimeglow/on_reaction)
  source file: Chemistry-Recipes.dm,1232
  usr: Cassidy Harshman (/mob/living/carbon/human)
  src: Slime Glow (/datum/chemical_reaction/slimeglow)
  call stack:
Slime Glow (/datum/chemical_reaction/slimeglow): on reaction(/datum/reagents (/datum/reagents), 1)
/datum/reagents (/datum/reagents): handle reactions()
/datum/reagents (/datum/reagents): trans to(the used slime extract (/obj/item/slime_extract/yellow), 5, 1, 1)
the syringe (/obj/item/weapon/reagent_containers/syringe): afterattack(the used slime extract (/obj/item/slime_extract/yellow), Cassidy Harshman (/mob/living/carbon/human), 1, "icon-x=15;icon-y=15;left=1;scr...")


--Fixed.