[NO SQUASH] Server: Correct client inventory prediction for IDropAction and IMoveAction

[SmallJoker]

Fixes the root cause of #15728.
The first commit is a cleanup of messy code that I encountered.

Details (same issue): #15728 (comment)

To do

This PR is Ready for Review.

How to test

diff --git a/src/network/serverpackethandler.cpp b/src/network/serverpackethandler.cpp
index 86c18725f..45fa8fa13 100644
--- a/src/network/serverpackethandler.cpp
+++ b/src/network/serverpackethandler.cpp
@@ -711,7 +711,8 @@ void Server::handleCommand_InventoryAction(NetworkPacket* pkt)
 		da->from_inv.applyCurrentPlayer(player->getName());
 
 		m_inventory_mgr->setInventoryModified(da->from_inv);
-		mark_player_inv_list_dirty(da->from_inv, da->from_list);
+		//mark_player_inv_list_dirty(da->from_inv, da->from_list);
+		return;
 
 		/*
 			Disable dropping items out of craftpreview

2. Drop an item. The inventory remains in an outdated state.
3. Uncomment the mark_player_inv_list_dirty line. The client prediction is now reverted.

[sfan5]

LGTM