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

@@ -2,18 +2,25 @@
 
 from gi.repository import Gio
 import sys
-import dbus
 
 def launch(desktop, *files):
     launcher = Gio.DesktopAppInfo.new_from_filename(desktop)
-    if hasattr(launcher, 'get_boolean'):
-        activatable = launcher.get_boolean('DBusActivatable')
-        if activatable:
-            bus = dbus.SessionBus()
-            service_id = launcher.get_id()
-            # cut the .desktop suffix
-            service_id = service_id[:-8]
-            bus.start_service_by_name(service_id)
+    try:
+        import dbus
+        if hasattr(launcher, 'get_boolean'):
+            activatable = launcher.get_boolean('DBusActivatable')
+            if activatable:
+                bus = dbus.SessionBus()
+                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__":