dbus: fix naming of multiple instances

The do-not-queue flag is necessary to ensure that the bus name is
obtained immediately or not at all. Without it, each VLC instances gets
put into the queue for the same name.

Also, failure must be checked from the return value of the function,
not (typically) the low-level error flag.

modules/control/dbus/dbus.c

@@ -193,14 +193,11 @@ static int Open( vlc_object_t *p_this )
             &dbus_mpris_vtable, p_this );
 
     /* Try to register org.mpris.MediaPlayer2.vlc */
+    const unsigned bus_flags = DBUS_NAME_FLAG_DO_NOT_QUEUE;
     var_Create(p_intf->obj.libvlc, "dbus-mpris-name", VLC_VAR_STRING);
-    dbus_bus_request_name( p_conn, DBUS_MPRIS_BUS_NAME, 0, &error );
-    if( dbus_error_is_set( &error ) )
+    if( dbus_bus_request_name( p_conn, DBUS_MPRIS_BUS_NAME, bus_flags, NULL )
+                                     != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER )
     {
-        msg_Dbg( p_this, "Failed to get service name %s: %s",
-                 DBUS_MPRIS_BUS_NAME, error.message );
-        dbus_error_free( &error );
-
         /* Register an instance-specific well known name of the form
          * org.mpris.MediaPlayer2.vlc.instanceXXXX where XXXX is the
          * current Process ID */
@@ -211,14 +208,8 @@ static int Open( vlc_object_t *p_this )
                   DBUS_MPRIS_BUS_NAME"."DBUS_INSTANCE_ID_PREFIX"%"PRIu32,
                   (uint32_t)getpid() );
 
-        dbus_bus_request_name( p_conn, unique_service, 0, &error );
-        if( dbus_error_is_set( &error ) )
-        {
-            msg_Err( p_this, "Failed to get service name %s: %s",
-                     DBUS_MPRIS_BUS_NAME, error.message );
-            dbus_error_free( &error );
-        }
-        else
+        if( dbus_bus_request_name( p_conn, unique_service, bus_flags, NULL )
+                                     == DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER )
         {
             msg_Dbg( p_intf, "listening on dbus as: %s", unique_service );
             var_SetString(p_intf->obj.libvlc, "dbus-mpris-name",