Fix: Add null checks for HTree and Pivot arrays before accessing them

[seer-by-sentry]

Fixes CLIENT-Q4. The issue was that: Read access violation in HTreeClass::Base_Update caused by null or corrupted HTree pointer during volumetric shadow transform validation.

• Added null checks for HTree in animobj.cpp and hlod.cpp to prevent crashes when accessing a null hierarchy tree.
• Added null and size checks for Pivot array in htree.cpp to prevent crashes when the array is invalid or empty.
• Added null checks for Parent pointer in htree.cpp to prevent crashes when accessing an invalid parent.
• Added null checks for Lod array and robj pointer in hlod.cpp to prevent crashes when accessing invalid LOD data or render objects.

This fix was generated by Seer in Sentry, triggered automatically. 👁️ Run ID: 2342019

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