branches/innodb+: btr_cur_search_to_nth_level(): Correct a merge

error.  In r2324, when changes were merged from branches/fts, the
assignment guess = NULL was accidentally removed after height--.
The assignment is in that place in branches/fts since r990.

btr/btr0cur.c

@@ -688,6 +688,7 @@ retry_page_get:
 	ut_ad(height > 0);
 
 	height--;
+	guess = NULL;
 
 	node_ptr = page_cur_get_rec(page_cursor);