added check for NULL callback_contact inside callback_disallow function.
added check for NULL callback_contact inside callback_disallow function.

globus/globus-toolkit,globus/globus-toolkit,globus/globus-toolkit,globus/globus-toolkit,gridcf/gct,ellert/globus-toolkit,ellert/globus-toolkit,gridcf/gct,ellert/globus-toolkit,ellert/globus-toolkit,ellert/globus-toolkit,gridcf/gct,gridcf/gct,globus/globus-toolkit,globus/globus-toolkit,ellert/globus-toolkit,globus/globus-toolkit,gridcf/gct,globus/globus-toolkit,ellert/globus-toolkit,ellert/globus-toolkit,gridcf/gct