A GLX surface can be in use by multiple VASurfaces, therefor make
sure refcounting is done properly. The code did not honor this and
could destroy a surface that was still in use by another GLX Surface
object.

The code is changed to enforce proper refcounting. Basically using

   destroy_glx_surface(driver_data, obj_glx_surface);

is suspicious and should be replaced by:

   glx_surface_unref(driver_data, obj_glx_surface);

instead. This function decreases the refcount on obj_glx_surface and
when it reaches 0, then it destroys the surface properly.