[205] Cannot mod SessionComponents_Economy.sbc - crashes

The crash:

Thread:   1 ->  Error: Error during loading session:System.OverflowException: Arithmetic operation resulted in an overflow.
   at System.Linq.Enumerable.Sum(IEnumerable`1 source)
   at Sandbox.Game.World.Generator.MyFactionGenerator.GenerateFactionsCount(MySessionComponentEconomyDefinition economyDefinition, List`1 factionTypes, Int32 factionsCount)
   at Sandbox.Game.World.Generator.MyFactionGenerator.GenerateFactions(MySessionComponentEconomyDefinition def)
   at Sandbox.Game.SessionComponents.MySessionComponentEconomy.BeforeStart()

The weird part is the mod has nothing to do with factions... at least not directly.

The steps to cause this crash:

1. Create a local mod folder: %appdata%/SpaceEngineers/Mods/YourMod/Data/

2. Copy the game's Data/Game/SessionComponents_Economy.sbc into that local mod's Data folder

3. Create a Star System world with that local mod present (economy generator has to run with the modded file)

The cause is that there's a MyFactionGenerator.LegacyModSupport() that reassigns faction types' ratios from the session component if it's a modded one, this is flawed because as you can see copying it from the game causes confusing problems.

The fix is very simple, if all the FactionRatio_* from the economy session definition are 0 then skip doing the LegacyModSupport() entirely.