Fix a crash while closing libnbc

If the free list initialization fails in libnbc_open()
mca_coll_libnbc_component.active_requests remain uninitialized,
resulting in a crash while closing the component

ompi/mca/coll/libnbc/coll_libnbc_component.c

@@ -88,13 +88,13 @@ libnbc_open(void)
     int ret;
 
     OBJ_CONSTRUCT(&mca_coll_libnbc_component.requests, opal_free_list_t);
+    OBJ_CONSTRUCT(&mca_coll_libnbc_component.active_requests, opal_list_t);
     ret = opal_free_list_init (&mca_coll_libnbc_component.requests,
                                sizeof(ompi_coll_libnbc_request_t), 8,
                                OBJ_CLASS(ompi_coll_libnbc_request_t),
                                0, 0, 0, -1, 8, NULL, 0, NULL, NULL, NULL);
     if (OMPI_SUCCESS != ret) return ret;
 
-    OBJ_CONSTRUCT(&mca_coll_libnbc_component.active_requests, opal_list_t);
     /* note: active comms is the number of communicators who have had
        a non-blocking collective started */
     mca_coll_libnbc_component.active_comms = 0;