BUG#16489 - utf8 + fulltext leads to corrupt index file.

Fixed that UPDATE statement crashes multi-byte charset fulltext index.

myisam/ft_update.c

@@ -170,6 +170,10 @@ int _mi_ft_cmp(MI_INFO *info, uint keynr, const byte *rec1, const byte *rec2)
   FT_SEG_ITERATOR ftsi1, ftsi2;
   CHARSET_INFO *cs=info->s->keyinfo[keynr].seg->charset;
   DBUG_ENTER("_mi_ft_cmp");
+#ifndef MYSQL_HAS_TRUE_CTYPE_IMPLEMENTATION
+  if (cs->mbmaxlen > 1)
+    DBUG_RETURN(THOSE_TWO_DAMN_KEYS_ARE_REALLY_DIFFERENT);
+#endif
 
   _mi_ft_segiterator_init(info, keynr, rec1, &ftsi1);
   _mi_ft_segiterator_init(info, keynr, rec2, &ftsi2);

mysql-test/r/fulltext2.result

@@ -234,5 +234,10 @@ insert into t1 values('test test '),('test'),('test'),('test'),
 ('test'),('test'),('test'),('test'),('test'),('test'),('test'),('test'),
 ('test'),('test'),('test'),('test'),('test'),('test'),('test'),('test');
 delete from t1 limit 1;
+truncate table t1;
+insert into t1 values('ab c d');
+update t1 set a='ab c d';
+select * from t1 where match a against('ab c' in boolean mode);
+a
 drop table t1;
 set names latin1;

mysql-test/t/fulltext2.test

@@ -209,6 +209,14 @@ insert into t1 values('test test '),('test'),('test'),('test'),
 ('test'),('test'),('test'),('test'),('test'),('test'),('test'),('test'),
 ('test'),('test'),('test'),('test'),('test'),('test'),('test'),('test');
 delete from t1 limit 1;
+
+#
+# BUG#16489: utf8 + fulltext leads to corrupt index file.
+#
+truncate table t1;
+insert into t1 values('ab c d');
+update t1 set a='ab c d';
+select * from t1 where match a against('ab c' in boolean mode);
 drop table t1;
 set names latin1;