Changed getStock to only return the actual stock they have left instead of the total amount of items left (and protected it)

src/main/java/com/alttd/playershops/shop/PlayerShop.java

@@ -84,8 +84,16 @@ public class PlayerShop {
         return playerShop;
     }
 
+    /**
+     * @return total amount of purchases left until the shop can't sell/buy anymore
+     */
     public int getRemainingStock() {
-        return InventoryUtils.countItems(getInventory(), getItemStack());
+        int totalItems = InventoryUtils.countItems(getInventory(), getItemStack());
+        if (totalItems == 0)
+            return 0;
+        if (getAmount() == 0)
+            return 0;
+        return totalItems / getAmount();
     }
 
     public int getRemainingSpace() {