Missing DC_EVENT_CHAT_MODIFIED event when dc_chat_can_send becomes true after secure join

- Operating System (Linux/Mac/Windows/iOS/Android): iOS
- Core Version: 2.35
- Client Version: deltachat-ios master

## Expected behavior

I expected a DC_EVENT_CHAT_MODIFIED event when dc_chat_can_send changes to true during secure join

## Actual behavior

Did not get any event even though can_send changed from false to true

### Steps to reproduce the problem

these steps are generic, see ios issue for steps on how to reproduce the UI bug that stems from this issue.

1. initiate securejoin
2. start listening for DC_EVENT_CHAT_MODIFIED
3. checked dc_chat_can_send, it still returns false
4. never receive DC_EVENT_CHAT_MODIFIED even though dc_chat_can_send becomes true at some point

https://github.com/deltachat/deltachat-ios/issues/2958