[FIX] mail: rename direct message chat

Before this commit, when a direct message chat was renamed, it
crashed with the following error:

`TypeError: Cannot read property 'toLowerCase' of undefined`

This occurs because the name of the dm chat changed from the RPC
response. However, no new name was provided, thus it sets its
name to `undefined`.

Test has been adapted in order to reflect that the server does not
response with new name after RPC `channel_set_custom_name`.

closes odoo/odoo#34641

Signed-off-by: Martin Geubelle (mge) <mge@openerp.com>

addons/mail/static/src/js/discuss.js

@@ -168,9 +168,9 @@ var RenameConversationDialog = Dialog.extend({
             kwargs: {
                 name: name,
             }
-        }).then(function (updatedName) {
+        }).then(function () {
             var channel = self.call('mail_service', 'getThread', self._channelID);
-            channel.setName(updatedName);
+            channel.setName(name);
             self._callback();
         });
     },

addons/mail/static/tests/discuss_tests.js

@@ -1507,7 +1507,7 @@ QUnit.test('rename DM conversation', function (assert) {
                 assert.step(args.method);
                 assert.strictEqual(args.args[0], 1);
                 assert.strictEqual(args.kwargs.name, "Demo");
-                return $.when("Demo");
+                return $.when();
             }
             return this._super.apply(this, arguments);
         },