Server class code cleanups (#9769)

* Server::overrideDayNightRatio doesn't require to return bool
There is no sense to sending null player, the caller should send a valid object

* Server::init: make private & cleanup
This function is always called before start() and loads some variables which can be loaded in constructor directly.
Make it private and call it directly in start

* Split Server inventory responsibility to a dedicated object

This splits permit to found various historical issues:
* duplicate lookups on player connection
* sending inventory to non related player when a player connects
* non friendly lookups on detached inventories ownership

This reduce the detached inventory complexity and also increased the
lookup performance in a quite interesting way for servers with thousands
of inventories.

src/server/serverinventorymgr.h

@@ -0,0 +1,60 @@
+/*
+Minetest
+Copyright (C) 2010-2020 Minetest core development team
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#pragma once
+
+#include "inventorymanager.h"
+#include <functional>
+
+class ServerEnvironment;
+
+class ServerInventoryManager : public InventoryManager
+{
+public:
+	ServerInventoryManager();
+	virtual ~ServerInventoryManager();
+
+	void setEnv(ServerEnvironment *env)
+	{
+		assert(!m_env);
+		m_env = env;
+	}
+
+	Inventory *getInventory(const InventoryLocation &loc);
+	void setInventoryModified(const InventoryLocation &loc);
+
+	// Creates or resets inventory
+	Inventory *createDetachedInventory(const std::string &name, IItemDefManager *idef,
+			const std::string &player = "");
+	bool removeDetachedInventory(const std::string &name);
+
+	void sendDetachedInventories(const std::string &peer_name, bool incremental,
+			std::function<void(const std::string &, Inventory *)> apply_cb);
+
+private:
+	struct DetachedInventory
+	{
+		Inventory *inventory;
+		std::string owner;
+	};
+
+	ServerEnvironment *m_env = nullptr;
+
+	std::unordered_map<std::string, DetachedInventory> m_detached_inventories;
+};