Stop the display after display server is stopped.

This is for recovering from display server crashes etc.

src/daemon/Display.cpp

@@ -60,8 +60,12 @@ namespace SDDM {
 
         m_display = QString(":%1").arg(m_displayNumber);
 
-        // connect signals
+        // stop the display after user session ends
         connect(m_authenticator, SIGNAL(stopped()), this, SLOT(stop()));
+
+        // stop the display after the display server stopped
+        connect(m_displayServer, SIGNAL(stopped()), this, SLOT(stop()));
+
         connect(m_socketServer, SIGNAL(login(QLocalSocket*,QString,QString,QString)), this, SLOT(login(QLocalSocket*,QString,QString,QString)));
 
         connect(this, SIGNAL(loginFailed(QLocalSocket*)), m_socketServer, SLOT(loginFailed(QLocalSocket*)));

src/daemon/DisplayServer.cpp

@@ -134,6 +134,9 @@ namespace SDDM {
         // clean up
         process->deleteLater();
         process = nullptr;
+
+        // emit signal
+        emit stopped();
     }
 
     bool DisplayServer::waitForStarted(int msecs) {

src/daemon/DisplayServer.h

@@ -41,6 +41,9 @@ namespace SDDM {
         void stop();
         void finished();
 
+    signals:
+        void stopped();
+
     private:
         bool waitForStarted(int msecs = 10000);