helper: Sync unread pm message count in all_pms and user button count.

[mkp6781]

User buttons list is updated using update_user_list before count of user
buttons is modified in _set_count_in_view. Now, we do not have to wait
for the presence update before displaying the correct unread count.

Fixes #438

[zulipbot]

Hello @mkp6781, it seems like you have referenced #438 in your pull request description, but you have not referenced them in your commit message description(s). When you reference an issue in a commit message, it automatically closes the corresponding issue when the commit is merged.

Please run git commit --amend in your command line client to amend your commit message description with Fixes #438..

An example of a correctly-formatted commit:

commit fabd5e450374c8dde65ec35f02140383940fe146
Author: zulipbot
Date:   Sat Mar 18 13:42:40 2017 -0700

    pull requests: Check PR commits reference when issue is referenced.

    Fixes #51.

Thank you for your contributions to Zulip!

[mkp6781]

@zulipbot add "PR needs review"

[zulipbot]

Heads up @mkp6781, we just merged some commits that conflict with the changes your made in this pull request! You can review this repository's recent commits to see where the conflicts occur. Please rebase your feature branch against the upstream/main branch and resolve your pull request's merge conflicts accordingly.