Fixes atmos processing race condition (#11447)

* Update atmosmachinery.dm

* Fixes preceding definition

* Update mixer.dm

* Removes unnecessary code

code/modules/atmospherics/machinery/components/trinary_devices/mixer.dm

@@ -63,7 +63,7 @@
 
 /obj/machinery/atmospherics/components/trinary/mixer/process_atmos()
 	..()
-	if(!on || !(nodes[1] && nodes[2] && nodes[3] && parents[1] && parents[2] && parents[3]) && !is_operational)
+	if(!on || !(nodes[1] && nodes[2] && nodes[3]) || !is_operational)
 		return
 
 	//Get those gases, mah boiiii