item_func.cc auto-init of ft-index restored (to cope with const/system tables)

sql/item_func.cc

@@ -1867,12 +1867,11 @@ err:
 
 double Item_func_match::val()
 {
-  /* If called uninitialized we should return neither NULL nor 0 (important
-     for const_tables) so, let's return -1, which is obviously incorrect
-     for normal operation, and could be easily spotted */
-
   if (ft_handler==NULL)
-    return -1.0;
+    init_search(1);
+
+  if (null_value=(ft_handler==NULL))
+    return 0.0;
 
   if (join_key)
   {