check if context->poll_chunk is set before trying to destroy it. For

check if context->poll_chunk is set before trying to destroy it. For

Wed Jul  9 16:27:26 2003  Manish Singh  <yosh@gimp.org>

        * glib/gmain.c (g_main_context_unref_and_unlock): check if
        context->poll_chunk is set before trying to destroy it. For example,
        This can happen if no sources are added to a context before it is
        freed.