[Bug] Crash when opening directory resource browser in Linux

[RevOcelotMGS]

Issue happens on both a built Linux version and emulated VIA Wine. Attempting to open the Directory Resource selection/browser causes this crash - using Arch Linux with KDE Plasma X11

***********SYSTEM INFO***********
OS: Microsoft Windows 10 Pro
GPU: ATI Radeon HD 5600 Series
UDB: R4128
Platform: x64

********EXCEPTION DETAILS********
Object reference not set to an instance of an object
  at CodeImp.DoomBuilder.Controls.Reflector.CallAs2 (System.Type type, System.Object obj, System.String func, System.Object[] parameters) [0x0000a] in <7c51038a0ef246f2b067745f44b7f735>:0 
  at CodeImp.DoomBuilder.Controls.Reflector.Call2 (System.Object obj, System.String func, System.Object[] parameters) [0x00007] in <7c51038a0ef246f2b067745f44b7f735>:0 
  at CodeImp.DoomBuilder.Controls.Reflector.Call (System.Object obj, System.String func, System.Object[] parameters) [0x00000] in <7c51038a0ef246f2b067745f44b7f735>:0 
  at CodeImp.DoomBuilder.Controls.FolderSelectDialog.ShowDialog (System.IntPtr hWndOwner) [0x00048] in <7c51038a0ef246f2b067745f44b7f735>:0 
  at CodeImp.DoomBuilder.Windows.ResourceOptionsForm.browsedir_Click (System.Object sender, System.EventArgs e) [0x0009a] in <7c51038a0ef246f2b067745f44b7f735>:0 
  at System.Windows.Forms.Control.OnClick (System.EventArgs e) [0x0001f] in <5ea26500d4d340168c8a375e356ca0ac>:0 
  at System.Windows.Forms.Button.OnClick (System.EventArgs e) [0x00037] in <5ea26500d4d340168c8a375e356ca0ac>:0 
  at System.Windows.Forms.Button.OnMouseUp (System.Windows.Forms.MouseEventArgs mevent) [0x0009a] in <5ea26500d4d340168c8a375e356ca0ac>:0 
  at System.Windows.Forms.Control.WmMouseUp (System.Windows.Forms.Message& m, System.Windows.Forms.MouseButtons button, System.Int32 clicks) [0x001c3] in <5ea26500d4d340168c8a375e356ca0ac>:0 
  at System.Windows.Forms.Control.WndProc (System.Windows.Forms.Message& m) [0x005a0] in <5ea26500d4d340168c8a375e356ca0ac>:0 
  at System.Windows.Forms.ButtonBase.WndProc (System.Windows.Forms.Message& m) [0x0011f] in <5ea26500d4d340168c8a375e356ca0ac>:0 
  at System.Windows.Forms.Button.WndProc (System.Windows.Forms.Message& m) [0x00056] in <5ea26500d4d340168c8a375e356ca0ac>:0 
  at System.Windows.Forms.Control+ControlNativeWindow.OnMessage (System.Windows.Forms.Message& m) [0x00001] in <5ea26500d4d340168c8a375e356ca0ac>:0 
  at System.Windows.Forms.Control+ControlNativeWindow.WndProc (System.Windows.Forms.Message& m) [0x000b3] in <5ea26500d4d340168c8a375e356ca0ac>:0 
  at System.Windows.Forms.NativeWindow.Callback (System.Windows.Forms.Message& m) [0x00025] in <5ea26500d4d340168c8a375e356ca0ac>:0 

Can continue from the crash in Wine, though Linux build fully crashes.

Screenshot attached for reference.