fix(gta-core-five): bound-check scenario point ped model set index

[DaniGP17]

Goal of this PR

CScenarioPoint::GetModelSetIndex() indexes m_ModelSets[kVehicleModelSets] for vehicle scenario points and m_ModelSets[kPedModelSets] for everything else, with no bounds check. Two call sites use it as a ped index without guarding on the scenario type, so a streamed AMBIENT_VEHICLE_MODEL_SET_FILE that grows the vehicle set count past the ped set count turns the mismatch into an OOB read.

Also fixes CAmbientModelSets::Append() nulling every model's Variations right after adopting it, which made resources streaming vehiclemodelsets.meta spawn the correct vehicle but always stock (mods/colours/livery never apply).

Used this resource for testing: https://github.com/lkid73/sete_le

How is this PR achieving the goal

Bound-checks CScenarioPoint::GetModelSetIndex() before it's used as a ped model set index, fixing an OOB read crash when a resource streams enough vehicle model sets to overflow the ped array.

Removes a ReleaseVariations() call in CAmbientModelSets::Append() that was nulling vehicle mods/colours/livery on load, so streamed vehicle model sets stopped spawning stock.

This PR applies to the following area(s)

FiveM

Successfully tested on

Game builds: 3407

Platforms: Windows

Checklist

• Code compiles and has been tested successfully.
• Code explains itself well and/or is documented.
• My commit message explains what the changes do and what they are for.
• No extra compilation warnings are added by these changes.

Fixes issues

fixes #3473