fix: dxDrawModel3D flickering issue

[naouh]

Summary

Fix dxDrawModel3D flickering when rendering a model

Motivation

Commit e5e308de1 ("GTA streamer bug-fix round #1") added ModelAddRef/RemoveRef inside RenderModel() to protect the RwObject from being GC'd during rendering. The problem is that RemoveRef does more than just decrement a counter, when MTA's m_dwReferences hits 0, it calls Remove(), which decrements GTA's usNumberOfRefs and if that also reaches 0, fires RemoveModel() and unloads the model.

With dxDrawModel3D, no persistent MTA-side reference is held, so every single frame:

1. ModelAddRef bumps refs 0 → 1
2. Model renders
3. RemoveRef drops refs 1 → 0 → Remove() → model unloaded
4. Next frame: model gone, EnqueueModel fails, nothing renders
5. engineStreamingRequestModel re-requests it, model reloads
6. Next frame: renders, then unloads again → repeat

Hence the flickering every other frame.

The fix replaces ModelAddRef/RemoveRef with a direct increment/decrement of GTA's usNumberOfRefs, which still blocks the streaming GC from freeing the model mid-render without triggering MTA's unload logic on release.

Test plan

Test with the Maybe v4 resource, objects that were flickering should now render stable.

[DM]Maybe_v4-_Saints_Boulevard.zip

Checklist

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