Initialize DBus object pointers with nullptr

This should fix a crash when the daemon is terminated before it can establish
connection and initialize the objects.

Signed-off-by: Mavridis Philippe <mavridisf@gmail.com>

src/portal_daemon.cpp

@@ -34,7 +34,12 @@
 
 PortalDaemon::PortalDaemon()
 : KUniqueApplication(),
-  m_retryCount(0)
+  m_retryCount(0),
+  d_root(nullptr),
+  d_org(nullptr),
+  d_freedesktop(nullptr),
+  d_portal(nullptr),
+  d_desktop(nullptr)
 {
     connectDBus();
 }