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

src/Utils/generics.ts

@@ -343,7 +343,7 @@ const STATUS_MAP: { [_: string]: proto.WebMessageInfo.Status } = {
  * @param type type from receipt
  */
 export const getStatusFromReceiptType = (type: string | undefined) => {
-	const status = STATUS_MAP[type ?? '']
+	const status = STATUS_MAP[type!]
 	if (typeof type === 'undefined') {
 		return proto.WebMessageInfo.Status.DELIVERY_ACK
 	}