Fix loading screen hanging on map parsing errors

[SadPencil]

This PR contains partial fix from #718

• Fix in some cases the loading screen might hang forever. Delay using XNAMessageBox as the DisplayErrorAction until the main menu has been loaded. Otherwise, if there are any exceptions be thrown when parsing the maps, the loading screen will hang for a long time (maybe forever but I am not sure).
• Add missing messages on existing Debug.Assert

[Copilot]

Pull Request Overview

This PR ensures the loading screen no longer hangs if map parsing errors occur by moving the error-display setup into the main menu initialization, and it enriches existing debug assertions with descriptive messages.

• Changed how and when DisplayErrorAction is assigned to prevent hangs on startup.
• Updated Debug.Assert calls to include explanatory messages in two channel‐related files.
• Tweaked exception logging null safety and made HandleException publicly accessible.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
DXMainClient/PreStartup.cs	Added null-conditional on TargetSite.Name, made HandleException public, used named parameter for clarity.
DXMainClient/Online/Channel.cs	Updated comment and added message string to Debug.Assert for users collection.
DXMainClient/DXGUI/Multiplayer/CnCNet/CnCNetLobby.cs	Added message string to Debug.Assert in RefreshPlayerList.
DXMainClient/DXGUI/Generic/MainMenu.cs	Moved DisplayErrorAction assignment into PostInit to defer error dialogs.
DXMainClient/DXGUI/GameClass.cs	Removed previous DisplayErrorAction assignment from Initialize.

Comments suppressed due to low confidence (2)

DXMainClient/PreStartup.cs:244

• Changing HandleException from static (package‐private) to public static alters the class's API surface. Confirm this exposure is intentional and update any documentation or consumers accordingly.

        public static void HandleException(object sender, Exception ex)

DXMainClient/DXGUI/Generic/MainMenu.cs:656

• This new error‐display behavior should be covered by unit or integration tests to verify that errors during map parsing invoke this DisplayErrorAction and that the application handles exit correctly.

            MainClientConstants.DisplayErrorAction = (title, error, exit) =>

[github-actions]

Nightly build for this pull request:

• artifacts.zip
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