[Bug]: setting_newgame console commands trigger post_cb callbacks which implicitly assume settings

[JGRennison]

Version of OpenTTD

master

Expected result

Use of the setting_newgame console command shouldn't effect changes as if the active settings were changed.

Actual result

Many of the post_cb implementations use a comparison between _game_mode and GM_MENU to decide whether the change should be effected on the running game and/or on _settings.

Use of setting_newgame as a multiplayer client can cause multiplayer desyncs or other state divergences.

Steps to reproduce

Use the setting_newgame console command.
Ones with interesting effects include: economy.minutes_per_calendar_year, service interval settings and freeform_edges.

[TrueBrain]

I never really understood why setting_newgame exists, but should it even be allowed in Multiplayer?

[JGRennison]

In principle you should be able to use it at any time because it should never affect the running game.
However I also doubt that this is used much or is really necessary.