[FIX] mail: chat window positioning with discuss open

Before this commit, the process of positioning chat windows
could fail if one of the tabs had discuss open.

When a chat window was hidden and become visible, the algorithm
was not updating the state of the chat window to "visible" when
discuss was open. As a result, it was always trying to make it
visible, resulting in an infinite loop and raising the following
error message:

`Uncaught RangeError: Maximum call stack size exceeded`

This commit ensures it works even when discuss is open.

opw-1919327

closes #30137

addons/mail/static/src/js/services/mail_window_manager.js

@@ -532,9 +532,6 @@ MailManager.include({
      * @private
      */
     _repositionThreadWindows: function () {
-        if (this._areAllThreadWindowsHidden()) {
-            return;
-        }
         this._computeAvailableSlotsForThreadWindows();
 
         this._repositionVisibleThreadWindows();
@@ -576,9 +573,6 @@ MailManager.include({
      *   the focus is on the thread window.
      */
     _updateThreadWindowsFromMessage: function (message, options) {
-        if (this._areAllThreadWindowsHidden()) {
-            return;
-        }
         _.each(this._threadWindows, function (threadWindow) {
             if (_.contains(message.getThreadIDs(), threadWindow.getID())) {
                 threadWindow.update(options);