MDEV-4257 Assertion `!table || (!table->read_set ||...

MDEV-4257 Assertion `!table || (!table->read_set || bitmap_is_set(table->read_set, field_index))' fails on FROM subquery with fulltext search, derived_merge=on

remove emtpty Item_func_match::update_used_tables() method

mysql-test/r/fulltext_derived_4257.result

+set optimizer_switch = 'derived_merge=on';
+create table t1 (c1 char(8), c2 char(8)) engine=myisam;
+insert into t1 values ('test1','test2'),('test3','test4');
+select * from (select c1 from t1 where match (c2) against ('hello' in boolean mode)) as alias;
+c1
+drop table t1;

mysql-test/t/fulltext_derived_4257.test

+set optimizer_switch = 'derived_merge=on';
+create table t1 (c1 char(8), c2 char(8)) engine=myisam;
+insert into t1 values ('test1','test2'),('test3','test4');
+select * from (select c1 from t1 where match (c2) against ('hello' in boolean mode)) as alias;
+drop table t1;
+

sql/item_func.h

@@ -1704,7 +1704,6 @@ public:
   bool is_expensive_processor(uchar *arg) { return TRUE; }
   enum Functype functype() const { return FT_FUNC; }
   const char *func_name() const { return "match"; }
-  void update_used_tables() {}
   table_map not_null_tables() const { return 0; }
   bool fix_fields(THD *thd, Item **ref);
   bool eq(const Item *, bool binary_cmp) const;