Fix wrong logic that disables "prevent sleeping" timer

Also update power management state early so we don't need to wait for
the timer timeout to have the effect.

src/gui/mainwindow.cpp

@@ -1454,9 +1454,12 @@ void MainWindow::loadPreferences(const bool configureSession)
 
     showStatusBar(pref->isStatusbarDisplayed());
 
-    if ((pref->preventFromSuspendWhenDownloading() || pref->preventFromSuspendWhenSeeding()) && !m_preventTimer->isActive()) {
+    if (pref->preventFromSuspendWhenDownloading() || pref->preventFromSuspendWhenSeeding()) {
+        if (!m_preventTimer->isActive()) {
+            updatePowerManagementState();
             m_preventTimer->start(PREVENT_SUSPEND_INTERVAL);
         }
+    }
     else {
         m_preventTimer->stop();
         m_pwr->setActivityState(false);