Crash when starting a free game

Describe the bug When starting a new game (FREE GAME from the main menu), the game crashes with this error:

Unhandled Exception:
System.NullReferenceException: Object reference not set to an instance of an object.
  at (wrapper managed-to-native) Godot.NativeCalls.godot_icall_2_378(intptr,intptr,intptr,bool)
  at Godot.Node.AddChild (Godot.Node node, System.Boolean legibleUniqueName) [0x00000] in /tmp/build_GodotSharp/GodotSharp/ObjectType/Node.cs:389 
  at RoomManager.ChangeRoom (System.String newRoomName, System.Boolean isAirport) [0x000a2] in /home/xerxes/Documents/coding/OpenATDeluxe/src/RoomManager.cs:77 
  at MainMenu+<>c.<.cctor>b__4_1 () [0x00001] in /home/xerxes/Documents/coding/OpenATDeluxe/src/Menus/MainMenu.cs:17 
  at CharacterItem._GuiInput (Godot.InputEvent e) [0x00035] in /home/xerxes/Documents/coding/OpenATDeluxe/src/CharacterItem.cs:32

To Reproduce

Select NEW GAME from the main menu

Expected behavior

The airport scene should load fine

Screenshots n/a

Desktop (please complete the following information):

OS: Linux Mint 19.1
Original Game Version: Deluxe
Version: Steam (BuildID 867111)

Additional context When forcing a game data import, the following warnings can be seen:

[...]
Error loading!
Error opening file: /home/xerxes/Downloads/Airline Tycoon Deluxe/data/clan.csv - Error FileCantOpen
  at BaseFileDecoder..ctor (System.String _filePath) [0x0002c] in /home/xerxes/Documents/coding/OpenATDeluxe/src/BaseFileDecoder.cs:28 
  at CSVFileDecoder..ctor (System.String _filePath) [0x00000] in /home/xerxes/Documents/coding/OpenATDeluxe/src/CSVFileDecoder.cs:10 
  at ClanCSVFile..ctor (System.String _filePath) [0x00000] in /home/xerxes/Documents/coding/OpenATDeluxe/src/ClanCSVFile.cs:17 
  at ATDGameLoader+<>c.<LoadOtherData>b__23_2 () [0x0000d] in /home/xerxes/Documents/coding/OpenATDeluxe/src/ATDGameLoader.cs:214 
  at ATDGameLoader.TryAction (System.Action action) [0x00002] in /home/xerxes/Documents/coding/OpenATDeluxe/src/ATDGameLoader.cs:178 
Error loading!
Error opening file: /home/xerxes/Downloads/Airline Tycoon Deluxe/data/brick.csv - Error FileCantOpen
  at BaseFileDecoder..ctor (System.String _filePath) [0x0002c] in /home/xerxes/Documents/coding/OpenATDeluxe/src/BaseFileDecoder.cs:28 
  at CSVFileDecoder..ctor (System.String _filePath) [0x00000] in /home/xerxes/Documents/coding/OpenATDeluxe/src/CSVFileDecoder.cs:10 
  at ATDGameLoader+<>c.<LoadOtherData>b__23_3 () [0x0000d] in /home/xerxes/Documents/coding/OpenATDeluxe/src/ATDGameLoader.cs:220 
  at ATDGameLoader.TryAction (System.Action action) [0x00002] in /home/xerxes/Documents/coding/OpenATDeluxe/src/ATDGameLoader.cs:178 
Wrong Texture Size! GFX: ZEIGER01
Wrong Texture Size! GFX: ZEIGER02
Wrong Texture Size! GFX: ZEIGER03
Wrong Texture Size! GFX: ZEIGER04
Wrong Texture Size! GFX: CONSTRUC
[...]

Excerpts from brick.csv and clan.csv (respectively):

Id;Beschreibung;RAM-Priority;opaque;Triggered;Layer;Speed;FloorDist;BaseX;BaseY;GridX;GridY;MinY;MaxY;Obstacle;TGA-Name
5000;Horizont1a;3;1;0;3;0;0;20;-18;88;1;132;132;0;BACK_A1
5001;Horizont1b;3;1;0;3;0;0;20;-18;88;1;132;132;0;BACK_A2
5002;Horizont2;4;1;0;3;0;0;20;-18;88;1;0;0;0;BACK_B
[...]

Typ;Group;Comment;Update;W'keit;Speed;Faktor;Koffer;Gimmik beim laufen oder Gimmick OffsetX;Gimmick beim warten oder Gimmick OffsetX;OffsetX;OffsetY;Palette;Norden;...;Anz;Osten;...;Anz;S<FC>den;...;Anz;Westen;...;Anz;Rennen: Norden;;Anz;Rennen: Osten;;Anz;Rennen: S<FC>den;;Anz;Rennen: Westen;;Anz;Gimmick;Anz;Winken;Anz;SitzenN;Anz;SitzenS;Anz;Stehen;Stehgimmick;Anz
10;-;Schwester Anne;0;100;3;3;-1;3;3;0;0;SCHW_PAL.LBM;SCHW_N01;SCHW_N01;3;SCHW_O01 SCHW_O02 SCHW_O03 SCHW_O04;SCHW_O01;6;SCHW_S01 SCHW_S02 SCHW_S03 SCHW_S04;SCHW_S01;3;SCHW_W01 SCHW_W02 SCHW_W03 SCHW_W04;SCHW_W01;6;SCHW_N01;SCHW_N01;3;SCHW_O01 SCHW_O02 SCHW_O03 SCHW_O04;SCHW_O01;6;SCHW_S01 SCHW_S02 SCHW_S03 SCHW_S04;SCHW_S01;3;SCHW_W01 SCHW_W02 SCHW_W03 SCHW_W04;SCHW_W01;6;SCHW_W03;-1;SCHW_W01;-1;SCHWSITN;-1;SCHWSITS;-1;SCHW_WN SCHW_WO SCHW_WS SCHW_WW;SCHW_WN;-1
-;-;-;-;-;-;-;-;-;-;0;0;-;SH_BIG;SH_BIG;1;SH_BIG;SH_BIG;1;SH_BIG;SH_BIG;1;SH_BIG;SH_BIG;1;SH_BIG;SH_BIG;1;SH_BIG;SH_BIG;1;SH_BIG;SH_BIG;1;SH_BIG;SH_BIG;1;SH_BIG;-1;SH_BIG;-1;SH_BIG;-1;SH_BIG;-1;SH_BIG SH_BIG SH_BIG SH_BIG;SH_BIG;-1
[...]

openairlinetycoon / OpenATDeluxe

Crash when starting a free game #21