Canisters are purchasable at cargo again (#71701)

## About The Pull Request

Checking the initial pack's contains did not work for canisters because
they were manually given a contains by ``generate_supply_packs()``, so
they were skipped over when creating supply packs.

## Why It's Good For The Game

Canisters can now be ordered again.

Closes https://github.com/tgstation/tgstation/issues/71679

## Changelog

🆑
fix: You can now order canisters again.
/🆑

code/controllers/subsystem/shuttle.dm

@@ -142,8 +142,6 @@ SUBSYSTEM_DEF(shuttle)
 	while(length(pack_processing))
 		var/datum/supply_pack/pack = pack_processing[length(pack_processing)]
 		pack_processing.len--
-		if(!initial(pack.contains))
-			continue
 		if(ispath(pack, /datum/supply_pack))
 			pack = new pack
 
@@ -152,6 +150,10 @@ SUBSYSTEM_DEF(shuttle)
 			pack_processing += generated_packs
 			continue
 
+		//we have to create the pack before checking if it has 'contains' because generate_supply_packs manually sets it, therefore we cant check initial.
+		if(!pack.contains)
+			continue
+
 		supply_packs[pack.id] = pack
 
 	setup_shuttles(stationary_docking_ports)