Fall back to direct execution when dbus is not installed or running

I have been using this with a dbus-less Gentoo template since the original
change, and have tested recently on whonix-gw with dbus enabled and running.

(cherry picked from commit bf69335074b45157734b881cc14d54ea43e7902a)

misc/qubesxdg.py

@@ -2,10 +2,11 @@
 
 from gi.repository import Gio
 import sys
-import dbus
 
 def launch(desktop, *files):
     launcher = Gio.DesktopAppInfo.new_from_filename(desktop)
+    try:
+        import dbus
         if hasattr(launcher, 'get_boolean'):
             activatable = launcher.get_boolean('DBusActivatable')
             if activatable:
@@ -13,7 +14,13 @@ def launch(desktop, *files):
                 service_id = launcher.get_id()
                 # cut the .desktop suffix
                 service_id = service_id[:-8]
+                try:
                     bus.start_service_by_name(service_id)
+                except dbus.DBusException:
+                    pass
+        return launcher.launch(files, None)
+    except ImportError:
+        pass
     launcher.launch(files, None)
 
 if __name__ == "__main__":