Fix empty our_pubkey in DirectMessagesModel

[hanton]

The PR is for solving https://github.com/damus-io/damus/issues/556

Root cause:

1. dms is created with empty pub key in HomeModel
2. After that, its pub key is never updated even when damus_state is updated in ContentView
3. The empty pub key of DirectMessagesModel is used to init a new DirectMessageModel, so the pub key of newly created DirectMessageModel is also empty
4. As a result, determine_is_request in DirectMessageModel will always return true because our_pubkey is empty.
5. It causes newly created conversations show in the Requests list, instead of DMs list

Input is welcome.

[jb55]

ohhh

[jb55]

sorry will get back to this soon