Auto-disable to auto-shutdown feature

src/qtlibtorrent/qbtsession.cpp

@@ -2068,6 +2068,8 @@ void QBtSession::readAlerts() {
           if(will_shutdown) {
             if(Preferences::shutdownWhenDownloadsComplete()) {
               qDebug("Preparing for auto-shutdown because all downloads are complete!");
+              // Disabling it for next time
+              Preferences::setShutdownWhenDownloadsComplete(false);
 #if LIBTORRENT_VERSION_MINOR < 15
               saveDHTEntry();
 #endif