fix looping over wrong number of edges

Author: molpopgen

c/tskit/trees.c

@@ -4615,7 +4615,7 @@ tsk_tree_seek_index(tsk_tree_t *self, tsk_size_t index, tsk_flags_t TSK_UNUSED(o
     }
 
     left = tree_index.tree_left[index];
-    for (i = 0; i < self->tree_sequence->num_trees; ++i) {
+    for (i = 0; i < self->tree_sequence->tables->edges.num_rows; ++i) {
         if (left >= edges_left[i] && left < edges_right[i]) {
             /* Should we assert that the cast is possible? */
             tsk_tree_insert_edge(self, edges_parent[i], edges_child[i], (tsk_id_t) i);