fix: resolve ephemeralMessage crash on iOS audio messages in getBase64FromMediaMessage

When processing iOS audio messages in getBase64FromMediaMessage, the subtype unwrapping loop assumed msg.message[subtype].message always exists if msg.message[subtype] is truthy. iOS ephemeral messages can have ephemeralMessage without the standard .message property, causing 'Cannot read properties of undefined' crashes.

- Add guard for msg.message being falsy before the loop
- Use optional chaining (msg.message[subtype]?.message) in the loop condition

Closes #2550

Author: gabrielgz0

src/api/integrations/channel/whatsapp/whatsapp.baileys.service.ts

@@ -4400,8 +4400,12 @@ export class BaileysStartupService extends ChannelStartupService {
         throw 'Message not found';
       }
 
+      if (!msg.message) {
+        throw 'Message not found';
+      }
+
       for (const subtype of MessageSubtype) {
-        if (msg.message[subtype]) {
+        if (msg.message[subtype]?.message) {
           msg.message = msg.message[subtype].message;
         }
       }