Fix segfault in WaterRenderObjClass when skybox asset fails to load

[1rgs]

Problem

On macOS (Apple Silicon, macos-vulkan preset, Beta 12), the game segfaults as soon as the shell map — or any map with water — renders:

Thread 0 Crashed (SIGSEGV, address 0x0):
  WaterRenderObjClass::Render(RenderInfoClass&)
  DefaultStaticSortListClass::Render_And_Clear(RenderInfoClass&)
  WW3D::Render_And_Clear_Static_Sort_Lists(RenderInfoClass&)
  RTS3DScene::Flush(RenderInfoClass&)
  ...

Root cause

WaterRenderObjClass::Render() dereferences m_skyBox whenever TheGlobalData->m_drawSkyBox is set, but Create_Render_Obj("new_skybox") returns null when the skybox asset is unavailable — e.g. when the base Generals archives aren't found at init (Steam layout without ZH_Generals/, or any partial-asset setup). Disassembly of the crash site confirms the null deref is the m_skyBox->Set_Position() / m_skyBox->Render() pair after the water-type switch.

replaceSkyboxTexture() has the same hazard: it passes m_skyBox into replacePrototypeTexture() → replaceAssetTexture(), which calls robj->Class_ID() unconditionally, so any map that swaps skybox textures crashes the same way.

Fix

• Guard the m_skyBox use in Render() (null check alongside the existing TheGlobalData check)
• Early-return in replaceSkyboxTexture() when m_skyBox is null
• Add [TEX_MISSING] stderr logging in Apply_Missing_Texture() (guarded #ifndef _WIN32), as proposed in the Session 44 notes — this is what made the missing-asset root cause diagnosable here

Testing

• Before: reproducible SIGSEGV on shell map load and on entering the USA campaign (macOS 26.5, M-series, Beta 12 + retail Steam ZH assets)
• After: shell map renders and plays fine; entering maps with water no longer crashes; when assets are complete the skybox renders as before (guard is a no-op)
• [TEX_MISSING] output confirmed: 247 missing textures with base archives absent → 1 (trstrtholecvr.tga, absent from retail archives) once ZH_Generals/ is in place

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