fix: revert remaining ?? '' patterns across Utils, WABinary, Signal, and WAUSync files
Completes the comprehensive revert of defensive null coalescing patterns
introduced in PRs 124-129. These patterns (e.g. `value ?? ''`) silently
produced empty strings instead of failing fast, causing subtle bugs like
malformed JIDs and broken Signal session lookups.
Files: libsignal.ts, messages-recv.ts, chat-utils.ts, generics.ts,
history.ts, messages-media.ts, messages.ts, process-message.ts,
validate-connection.ts, jid-utils.ts, UsyncBotProfileProtocol.ts
https://claude.ai/code/session_01XaA7GwNaB6azTHFYQ8WEpB
Claude
2a9d9a0a52