Fix vending machines throwing (#1225)

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.IntegrationTests/Tests/VendingMachineTest.cs

@@ -0,0 +1,41 @@
+using System.Threading.Tasks;
+using Content.Shared.VendingMachines;
+using NUnit.Framework;
+using Robust.Shared.GameObjects;
+using Robust.Shared.IoC;
+using Robust.Shared.Prototypes;
+
+namespace Content.IntegrationTests.Tests
+{
+    [TestFixture]
+    [TestOf(typeof(VendingMachineInventoryPrototype))]
+    public sealed class VendingMachineTest : ContentIntegrationTest
+    {
+        [Test]
+        public async Task Test()
+        {
+            var server = StartServerDummyTicker();
+            
+            server.Assert(() =>
+            {
+                var prototypeManager = IoCManager.Resolve<IPrototypeManager>();
+                foreach (var vendorProto in prototypeManager.EnumeratePrototypes<VendingMachineInventoryPrototype>())
+                {
+                    foreach (var (item, _) in vendorProto.StartingInventory)
+                    {
+                        try
+                        {
+                            prototypeManager.Index<EntityPrototype>(item);
+                        }
+                        catch (UnknownPrototypeException)
+                        {
+                            throw new UnknownPrototypeException($"Unknown prototype {item} on vending inventory {vendorProto.Name}");
+                        }
+                    }
+                }
+            });
+
+            await server.WaitIdleAsync();
+        }
+    }
+}