Core/Vendors: Support for vendors with empty inventory list

Port From (https://github.com/TrinityCore/TrinityCore/commit/bedc0503578b220b19d23559f670f65d26c8bc87)

Source/Framework/Constants/CreatureConst.cs

@@ -149,7 +149,7 @@ namespace Framework.Constants
     }
 
     public enum NPCFlags2
-    { 
+    {
         None = 0x00,
         ItemUpgradeMaster = 0x01,
         GarrisonArchitect = 0x02,
@@ -394,4 +394,10 @@ namespace Framework.Constants
 
         Max
     }
+
+    public enum VendorInventoryReason
+    {
+        None = 0,
+        Empty = 1
+    }
 }

Source/Game/Entities/Player/Player.cs

@@ -2294,14 +2294,6 @@ namespace Game.Entities
                             if (!IsDead())
                                 canTalk = false;
                             break;
-                        case GossipOption.Vendor:
-                            VendorItemData vendorItems = creature.GetVendorItems();
-                            if (vendorItems == null || vendorItems.Empty())
-                            {
-                                Log.outError(LogFilter.Sql, "Creature (GUID: {0}, Entry: {1}) have UNIT_NPC_FLAG_VENDOR but have empty trading item list.", creature.GetGUID().ToString(), creature.GetEntry());
-                                canTalk = false;
-                            }
-                            break;
                         case GossipOption.Learndualspec:
                             canTalk = false;
                             break;
@@ -2324,8 +2316,9 @@ namespace Game.Entities
                         case GossipOption.Questgiver:
                             canTalk = false;
                             break;
-                        case GossipOption.Trainer:
                         case GossipOption.Gossip:
+                        case GossipOption.Vendor:
+                        case GossipOption.Trainer:
                         case GossipOption.Spiritguide:
                         case GossipOption.Innkeeper:
                         case GossipOption.Banker:

Source/Game/Handlers/NPCHandler.cs

@@ -564,6 +564,8 @@ namespace Game
                     break;
             }
 
+            packet.Reason = (byte)(count != 0 ? VendorInventoryReason.None : VendorInventoryReason.Empty);
+
             SendPacket(packet);
         }
     }