Update canister icons when connected to a port (#43518)

I found that when the valve of a canister was closed, the
.../canister/process_atmos proc would never reach its update_icon call.
I've fixed that by removing the early return and having a single
update_icon call at the end run when necessary.

code/modules/atmospherics/machinery/portable/canister.dm

@@ -366,19 +366,19 @@
 	if(timing && valve_timer < world.time)
 		valve_open = !valve_open
 		timing = FALSE
-	if(!valve_open)
+	if(valve_open)
+		var/turf/T = get_turf(src)
+		pump.airs[1] = air_contents
+		pump.airs[2] = holding ? holding.air_contents : T.return_air()
+		pump.target_pressure = release_pressure
+
+		pump.process_atmos() // Pump gas.
+		if(!holding)
+			air_update_turf() // Update the environment if needed.
+	else
 		pump.airs[1] = null
 		pump.airs[2] = null
-		return
-
-	var/turf/T = get_turf(src)
-	pump.airs[1] = air_contents
-	pump.airs[2] = holding ? holding.air_contents : T.return_air()
-	pump.target_pressure = release_pressure
 
-	pump.process_atmos() // Pump gas.
-	if(!holding)
-		air_update_turf() // Update the environment if needed.
 	update_icon()
 
 /obj/machinery/portable_atmospherics/canister/ui_interact(mob/user, ui_key = "main", datum/tgui/ui = null, force_open = FALSE, \