使用jitsi调用retrieveParticipantsInfo时ExternalAPI文件崩溃

### Steps to reproduce

When I first enter the meeting and call the retrieveParticipantsInfo method to get people, after calling the leave method, after rejoining the meeting, the retrieveP


https://github.com/user-attachments/assets/5715e242-767c-4210-ab14-b6fd73493918

### Outcome

希望能正常获取到当前的参会人员

### Your phone model

各类型的手机型号

### Operating system version

iOS 16

### Application version

0.27.8

### Homeserver

_No response_

### Will you send logs?

Yes

Start by locating the ExternalAPI implementation and the retrieveParticipantsInfo call path in the iOS app. Reproduce the sequence on iOS 16 with Element 0.27.8: join, retrieve participants, leave, then rejoin; inspect the available logs around the crash. Done means the second call returns the current participants without crashing.

Written by the indexing model from the issue text.