Enhance LOD model ID handling for entities

[Zephkek]

Summary

Makes processLineOfSight and testSphereAgainstWorld return the entity's own model ID when a ray hits a LOD entity directly, instead of returning 0.

Motivation

Follow-up to #4863. For co-located HD/LOD placements (e.g., billboards), rays that hit the LOD entity itself previously returned worldLODModelID = 0 because LODs naturally have m_pLod == NULL.

This patch fixes that by checking if the hit entity is a LOD (numLodChildren > 0) and reporting its own ID. Standard non-LOD buildings (numLodChildren == 0) are unaffected and still correctly return 0.

Test Plan

• Shared LODs (BillBd3): Consistently returns LOD ID 1266 from all angles, regardless of whether the ray hits the HD or LOD entity first.
• Singleton pairs & plain buildings: Unchanged; standard buildings still return 0.
• Scripted low-LOD objects: Unaffected (still use m_pLod).

Checklist

• Code follows guidelines
• Reviewable commit-by-commit