Don't overwrite stored layout of main window with incorrect one

Prevents overwriting of the stored layout in case the main window was hidden at startup and
has not been shown since, because incorrect dimensions can be provided by it in this case.

PR qbittorrent#20725.
Closes qbittorrent#20720.

src/gui/mainwindow.cpp

@@ -796,8 +796,11 @@ void MainWindow::saveSplitterSettings() const
 
 void MainWindow::cleanup()
 {
-    saveSettings();
-    saveSplitterSettings();
+    if (!m_neverShown)
+    {
+        saveSettings();
+        saveSplitterSettings();
+    }
 
     // delete RSSWidget explicitly to avoid crash in
     // handleRSSUnreadCountUpdated() at application shutdown