fix: Guard BodyModule access in StealthUpdate::allowedToStealth

[seer-by-sentry]

This PR addresses issue CLIENT-4ZV, which was an EXCEPTION_ACCESS_VIOLATION_READ at 0x0 in StealthUpdate::allowedToStealth.

The root cause was identified as a NULL pointer dereference when self->getBodyModule() returned NULL for objects lacking a BodyModule, and getLastDamageTimestamp() was called on the resulting NULL pointer. Additionally, a potential secondary NULL dereference was identified if getBodyModule()->getLastDamageInfo() returned NULL (which it does for base BodyModule implementations).

The fix involves:

1. Caching the result of self->getBodyModule() into a local pointer (body).
2. Adding a NULL check for body before attempting to call body->getLastDamageTimestamp() in the STEALTH_NOT_WHILE_TAKING_DAMAGE condition.
3. Adding a NULL check for body->getLastDamageInfo() before dereferencing it, to prevent crashes for objects with non-ActiveBody modules.

These changes ensure that getLastDamageTimestamp() and getLastDamageInfo() are only called on valid BodyModuleInterface pointers.

Fixes CLIENT-4ZV

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