ospf6d: Fix memory allocation issues in SPF

* ospf6_area.c: Call ospf6_spf_table_finish() before deleting the spf
    table.  This ensures that the associated ospf6_vertex structures
    are also freed.
* ospf6_spf.c: Only allocate a priority queue when a spf calculation
    is actually performed.  Also defer calling ospf6_spf_table_finish().
diff --git a/ospf6d/ospf6_spf.c b/ospf6d/ospf6_spf.c
index 04367f0..cb54961 100644
--- a/ospf6d/ospf6_spf.c
+++ b/ospf6d/ospf6_spf.c
@@ -392,18 +392,19 @@
   caddr_t lsdesc;
   struct ospf6_lsa *lsa;
 
-  /* initialize */
-  candidate_list = pqueue_create ();
-  candidate_list->cmp = ospf6_vertex_cmp;
-
-  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),
                            router_id, oa->lsdb);
   if (lsa == NULL)
     return;
+
+  /* initialize */
+  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;