Add empty signal payload validation

[seer-by-sentry]

Fixes CLIENT-295. The issue was that: Empty P2P signaling payload passed to OpenSSL's OSSL_CMP_validate_msg causes integer division by zero.

• Added validation to prevent empty signal payloads from being processed.
• Empty signal payloads are now ignored or skipped with a warning log.
• Prevents potential crashes related to OpenSSL CMP validation when handling empty signal data.

This fix was generated by Seer in Sentry, triggered automatically. 👁️ Run ID: 8436508

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