Vendor Exploit Fix (#1967)

Fixes a pretty severe exploit where spambuying from a vendor allows you to purchase a larger quantity than the vendor has. Coupled with the ability to add things, this is basically infinite item duplication. How did we not notice this before now?

I kept the spam buying, because it's pretty nifty, but added a safety check to ensure there's one remaining to buy

In addition, adds a little exception that allows bluespace technicians to take free stuff from vendors. Largely for debugging. I'm sick of having to spawn as a crewmember to do anything vendor related, this will save a bit of development time in the long run.

code/game/machinery/vending.dm

@@ -181,6 +181,13 @@
 		var/paid = 0
 		var/handled = 0
 
+		if (currently_vending.amount < 1)
+			visible_message(span("warning","\The [src] buzzes and flashes a message on its LCD: <b>\"Out of stock.\"</b>"))
+			src.status_error = 1
+			playsound(src.loc, 'sound/machines/buzz-two.ogg', 35, 1)
+			currently_vending = null
+			return
+
 		if (I) //for IDs and PDAs and wallets with IDs
 			paid = pay_with_card(I,W)
 			handled = 1
@@ -321,6 +328,10 @@
 		visible_message("<span class='info'>\The [usr] swipes \the [ID_container] through \the [src].</span>")
 	var/datum/money_account/customer_account = get_account(I.associated_account_number)
 	if (!customer_account)
+		//Allow BSTs to take stuff from vendors, for debugging and adminbus purposes
+		if (istype(I, /obj/item/weapon/card/id/bst))
+			return 1
+
 		src.status_message = "Error: Unable to access account. Please contact technical support if problem persists."
 		src.status_error = 1
 		return 0
@@ -507,6 +518,9 @@
 		nanomanager.update_uis(src)
 
 /obj/machinery/vending/proc/vend(datum/data/vending_product/R, mob/user)
+	if (!R || R.amount < 1)
+		return
+
 	if((!allowed(usr)) && !emagged && scan_id)	//For SECURE VENDING MACHINES YEAH
 		usr << "<span class='warning'>Access denied.</span>"	//Unless emagged of course
 		flick(src.icon_deny,src)
@@ -516,6 +530,8 @@
 	src.status_error = 0
 	nanomanager.update_uis(src)
 
+
+
 	if (R.category & CAT_COIN)
 		if(!coin)
 			user << "<span class='notice'>You need to insert a coin to get this item.</span>"