chat: fix issues with the initial "New Chat"

[cebtenzzre]

At startup:

• Wait until the conversationList view has been connected to the ChatListModel before adding any chats to the list. Otherwise, the initial "New Chat" tends to be scrolled just above the top of the view if the user has enough chats.

When the "New chat" button is clicked:

• If there is already a new chat, select the existing new chat instead of doing nothing. Buttons that do nothing are frustrating.
• When the new chat button is clicked, always scroll to the top of the list, so the chat is visible.

Also, make the connections to ChatRestoreThread explicitly queued. I'm pretty sure m_chats was being modified from more than one thread without this change.

[manyoso]

I'd like to huddle about this one as well, because I'm not sure what this is fixing and I have questions that the explicit queuing of the connection is needed. To be sure, there is nothing wrong with making it explicitly queued, but I'd like to investigate to be sure this is actually necessary.

[cebtenzzre]

I have questions that the explicit queuing of the connection is needed. To be sure, there is nothing wrong with making it explicitly queued, but I'd like to investigate to be sure this is actually necessary.

Heh, because this codebase is full of Qt::QueuedConnection whenever threads are involved, I didn't realize that Qt automatically queues signals when the sender and receiver are in different threads. Not actually a necessary change then, but probably good to have for consistency.