[Bug] Item Purchase Offset when multiple buyers are buying at the same time. (#4628)

* [Bug] Item Purchase Offset when multiple buyers are buying at the same time.

- Much of the code lifted from TAKP/P2002 and adapted
- Needs Testing
- This should help prevent situations where multiple people are purchasing items from a merchant and both attempt to purchase the same temp merchant or limited item, it should result in the later person recieving a notice that the item no longer exists and refreshes the merchant table.
- Updated strings

* fix formatting

* Push

* Update client.cpp

* Update database_update_manifest.cpp

* Update database_update_manifest.cpp

* Update database_update_manifest.cpp

* Update client.cpp

---------

Co-authored-by: Kinglykrab <kinglykrab@gmail.com>
Co-authored-by: Akkadius <akkadius1@gmail.com>

zone/entity.cpp

@@ -5950,3 +5950,53 @@ std::vector<NPC*> EntityList::GetExcludedNPCsByIDs(std::vector<uint32> npc_ids)
 
 	return v;
 }
+
+void EntityList::SendMerchantEnd(Mob* merchant)
+{
+	for (const auto& e : client_list) {
+		Client* c = e.second;
+
+		if (!c) {
+			continue;
+		}
+
+		if (c->GetMerchantSessionEntityID() == merchant->GetID()) {
+			c->SendMerchantEnd();
+		}
+	}
+}
+
+void EntityList::SendMerchantInventory(Mob* m, int32 slot_id, bool is_delete)
+{
+	if (!m || !m->IsNPC()) {
+		return;
+	}
+
+	for (const auto& e : client_list) {
+		Client* c = e.second;
+
+		if (!c) {
+			continue;
+		}
+
+		if (c->GetMerchantSessionEntityID() == m->GetID()) {
+			if (!is_delete) {
+				c->BulkSendMerchantInventory(m->CastToNPC()->MerchantType, m->GetNPCTypeID());
+			} else {
+				auto app = new EQApplicationPacket(OP_ShopDelItem, sizeof(Merchant_DelItem_Struct));
+				auto d   = (Merchant_DelItem_Struct*)app->pBuffer;
+
+				d->itemslot   = slot_id;
+				d->npcid      = m->GetID();
+				d->playerid   = c->GetID();
+
+				app->priority = 6;
+
+				c->QueuePacket(app);
+				safe_delete(app);
+			}
+		}
+	}
+
+	return;
+}