[FIX] mail: Discuss: apply default filters

Before this rev., the default filters were ignored in Discuss. The
SearchView was instantiated and correctly retrieved the default
filters. However, a first manual 'do_search' needs to be done by
the client action for the search view to provide the domain, and
for Discuss to correctly filter the messages.

Steps to reproduce the issue:
  - In Discuss (e.g. in Inbox), add to Favorites a given search,
    and tick 'Use by default'
  - Leave Discuss, and then go back: the default filter correctly
    appears in the search view, but the messages aren't filtered.

addons/mail/static/src/js/client_action.js

@@ -231,6 +231,9 @@ var ChatAction = Widget.extend(ControlPanelMixin, {
         var def3 = this.extended_composer.appendTo(this.$('.o_mail_chat_content'));
         var def4 = this.searchview.appendTo($("<div>")).then(function () {
             self.$searchview_buttons = self.searchview.$buttons.contents();
+            // manually call do_search to generate the initial domain and filter
+            // the messages in the default channel
+            self.searchview.do_search();
         });
 
         this.render_sidebar();
@@ -547,7 +550,12 @@ var ChatAction = Widget.extend(ControlPanelMixin, {
         });
 
         this.domain = result.domain;
-        this.fetch_and_render_thread();
+        if (this.channel) {
+            // initially (when do_search is called manually), there is no
+            // channel set yet, so don't try to fetch and render the thread as
+            // this will be done as soon as the default channel is set
+            this.fetch_and_render_thread();
+        }
     },
 
     on_post_message: function (message) {