Bug#14616 - Freshly imported table returns error 124 when using LIMIT

Initialized usable_keys from table->keys_in_use instead of ~0
in test_if_skip_sort_order(). It was possible that a disabled
index was used for sorting.

mysql-test/r/myisam.result

@@ -462,3 +462,13 @@ select count(*) from t1 where a is null;
 count(*)
 2
 drop table t1;
+create table t1 (
+c1 varchar(32),
+key (c1)
+) engine=myisam;
+alter table t1 disable keys;
+insert into t1 values ('a'), ('b');
+select c1 from t1 order by c1 limit 1;
+c1
+a
+drop table t1;

mysql-test/t/myisam.test

@@ -446,3 +446,15 @@ explain select count(*) from t1 where a is null;
 select count(*) from t1 where a is null;
 drop table t1;
 
+#
+# Bug#14616 - Freshly imported table returns error 124 when using LIMIT
+#
+create table t1 (
+  c1 varchar(32),
+  key (c1)
+) engine=myisam;
+alter table t1 disable keys;
+insert into t1 values ('a'), ('b');
+select c1 from t1 order by c1 limit 1;
+drop table t1;
+

sql/sql_select.cc

@@ -6003,8 +6003,12 @@ test_if_skip_sort_order(JOIN_TAB *tab,ORDER *order,ha_rows select_limit,
   key_map usable_keys;
   DBUG_ENTER("test_if_skip_sort_order");
 
-  /* Check which keys can be used to resolve ORDER BY */
-  usable_keys= ~(key_map) 0;
+  /*
+    Check which keys can be used to resolve ORDER BY.
+    We must not try to use disabled keys.
+  */
+  usable_keys= table->keys_in_use;
+
   for (ORDER *tmp_order=order; tmp_order ; tmp_order=tmp_order->next)
   {
     if ((*tmp_order->item)->type() != Item::FIELD_ITEM)