A fix (Bug #5428 small max_sort_length crash server).

mysql-test/r/order_by.result

@@ -723,3 +723,16 @@ col2	col	col
 2	2	2
 1	3	3
 drop table t1, t2;
+create table t1 (a char(25));
+insert into t1 set a = repeat('x', 20);
+insert into t1 set a = concat(repeat('x', 19), 'z');
+insert into t1 set a = concat(repeat('x', 19), 'ab');
+insert into t1 set a = concat(repeat('x', 19), 'aa');
+set max_sort_length=20;
+select a from t1 order by a;
+a
+xxxxxxxxxxxxxxxxxxxab
+xxxxxxxxxxxxxxxxxxxaa
+xxxxxxxxxxxxxxxxxxxx
+xxxxxxxxxxxxxxxxxxxz
+drop table t1;

mysql-test/t/order_by.test

@@ -486,3 +486,16 @@ select t2.col2 as col, t2.col from t2 order by t2.col;
 select t2.col2, t2.col, t2.col from t2 order by t2.col;
 
 drop table t1, t2;
+
+#
+# Bug #5428: a problem with small max_sort_length value
+#
+
+create table t1 (a char(25));
+insert into t1 set a = repeat('x', 20);
+insert into t1 set a = concat(repeat('x', 19), 'z');
+insert into t1 set a = concat(repeat('x', 19), 'ab');
+insert into t1 set a = concat(repeat('x', 19), 'aa');
+set max_sort_length=20;
+select a from t1 order by a;
+drop table t1;

strings/ctype-simple.c

@@ -27,8 +27,7 @@ int my_strnxfrm_simple(CHARSET_INFO * cs,
                        const uchar *src, uint srclen)
 {
   uchar *map= cs->sort_order;
-  DBUG_ASSERT(len >= srclen);
-  len= min(len,srclen);
+  set_if_smaller(len, srclen);
   if (dest != src)
   {
     const uchar *end;