When player position desyncs ensure position.old is also updated

Source/multi.cpp

@@ -657,6 +657,7 @@ void multi_process_network_packets()
 						player.position.future = syncPosition;
 						if (player.isWalking())
 							player.position.temp = syncPosition;
+						SetPlayerOld(player);
 						dPlayer[player.position.tile.x][player.position.tile.y] = playerId + 1;
 					}
 					if (player.position.future.WalkingDistance(player.position.tile) > 1) {
@@ -668,6 +669,7 @@ void multi_process_network_packets()
 				} else {
 					player.position.tile = syncPosition;
 					player.position.future = syncPosition;
+					SetPlayerOld(player);
 				}
 			}
 		}

Source/player.cpp

@@ -2588,6 +2588,7 @@ void InitPlayer(Player &player, bool firstTime)
 		}
 
 		player.position.future = player.position.tile;
+		SetPlayerOld(player);
 		player.walkpath[0] = WALK_NONE;
 		player.destAction = ACTION_NONE;
 
@@ -2701,6 +2702,16 @@ void FixPlrWalkTags(const Player &player)
 			dPlayer[searchTile.x][searchTile.y] = 0;
 		}
 	}
+
+#ifdef _DEBUG
+	// Checks that FixPlrWalkTags really removes player from all dPlayer tiles
+	// FixPlrWalkTags could fail if player.position.old is not updated correctly
+	for (int y = 0; y < MAXDUNY; y++) {
+		for (int x = 0; x < MAXDUNX; x++) {
+			assert(PlayerAtPosition({ x, y }) != &player);
+		}
+	}
+#endif
 }
 
 void StartPlrHit(Player &player, int dam, bool forcehit)