ospf6d: always remove the result of a previous SPF calculation

This is needed to avoid stale routes in some cases; the regression was
introduced by commit 1d19234e79c77a7d55194b513f2a77c6a691bc2c.

* ospf6_spf.c: (ospf6_spf_calculation) Call ospf6_spf_table_finish()
  before possibly returning if no router-LSA is found for the root of
  the SPF tree.
diff --git a/ospf6d/ospf6_spf.c b/ospf6d/ospf6_spf.c
index beb6d7f..a4a5b72 100644
--- a/ospf6d/ospf6_spf.c
+++ b/ospf6d/ospf6_spf.c
@@ -391,6 +391,8 @@
   caddr_t lsdesc;
   struct ospf6_lsa *lsa;
 
+  ospf6_spf_table_finish (result_table);
+
   /* Install the calculating router itself as the root of the SPF tree */
   /* construct root vertex */
   lsa = ospf6_lsdb_lookup (htons (OSPF6_LSTYPE_ROUTER), htonl (0),
@@ -402,8 +404,6 @@
   candidate_list = pqueue_create ();
   candidate_list->cmp = ospf6_vertex_cmp;
 
-  ospf6_spf_table_finish (result_table);
-
   root = ospf6_vertex_create (lsa);
   root->area = oa;
   root->cost = 0;