winebus.sys: Don't do anything in udev_driver_unload if udev was not initialized.

Signed-off-by: Piotr Caban <piotr@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

dlls/winebus.sys/bus_udev.c

@@ -1488,6 +1488,9 @@ void udev_driver_unload( void )
 {
     TRACE("Unload Driver\n");
 
+    if (!deviceloop_handle)
+        return;
+
     write(deviceloop_control[1], "q", 1);
     WaitForSingleObject(deviceloop_handle, INFINITE);
     close(deviceloop_control[0]);