Set new_game before loading JSON data

[RenechCDDA]

Summary

None

Purpose of change

• Fixes Game crashes generating faction camp recipes when any of the components has_temperature() #50493
• Resolves blocker for add earthworms and their delicacies #71804

While loading core data, we do some adjustments to the (fake) map (yes before the game is started!). But we only set new_game after loading the json, but still before we actually start the game. The assumption being that loading json data is just loading json data, it doesn't modify the map or do anything besides moving data around. Well, it does. Camps generate a fake map, perform fake map updates to it, and in the process (about 20 functions down the callstack, in weather_manager::get_temperature) process any items with temperature that those fake updates generated. Since the real map isn't loaded and doesn't exist, it crashes.

Describe the solution

Before loading the JSON data, set new_game. This prevents the call in weather_manager::get_temperature and is what I personally would expect to be the case. new_game is still set to false at the same time(when the game is actually started), so this shouldn't impact gameplay. The only chance for unexpected interactions is if some function explicitly relied on new_game being false during loading(?!), which would be a baffling circumstance.

There are very few places where new_game is checked, so I am pretty confident this is a safe change.

Describe alternatives you've considered

I tried changing the default parameters for mapgendata to use a terrain type which wouldn't generate any items, but this wasn't successful. The byproducts of the fake camp update were still being generated. I tried again, using a completely null terrain which couldn't be loaded, same issue.

Testing

All tests besides localization/overmap test passed locally, both before and after the changes. Game compiles, loads, does not crash even with the linked issue's JSON loaded.

Additional context

[juur]

This resolves the block on #71804 when applied locally.