Fixed bug #20076.

Server crashed in some cases when a query required a MIN/MAX
agrregation for a 'ucs2' field. 
In these cases  the aggregation caused calls of the function
update_tmptable_sum_func that indirectly invoked 
the method Item_sum_hybrid::min_max_update_str_field() 
containing a call to strip_sp for a ucs2 character set.
The latter led directly to the crash as it used my_isspace
undefined for the ucs2 character set.
Actually the call of strip_sp is not needed at all in this
situation and has been removed by the fix.

mysql-test/r/ctype_ucs.result

@@ -715,3 +715,10 @@ lily
 river
 drop table t1;
 deallocate prepare stmt;
+CREATE TABLE t1 (id int, s char(5) CHARACTER SET ucs2 COLLATE ucs2_unicode_ci);
+INSERT INTO t1 VALUES (1, 'ZZZZZ'), (1, 'ZZZ'), (2, 'ZZZ'), (2, 'ZZZZZ');
+SELECT id, MIN(s) FROM t1 GROUP BY id;
+id	MIN(s)
+1	ZZZ
+2	ZZZ
+DROP TABLE t1;

mysql-test/t/ctype_ucs.test

@@ -451,4 +451,16 @@ execute stmt using @param1;
 select utext from t1 where utext like '%%';
 drop table t1;
 deallocate prepare stmt;
+
+#
+# Bug #20076: server crashes for a query with GROUP BY if MIN/MAX aggregation
+#             over a 'ucs2' field uses a temporary table 
+#
+
+CREATE TABLE t1 (id int, s char(5) CHARACTER SET ucs2 COLLATE ucs2_unicode_ci);
+INSERT INTO t1 VALUES (1, 'ZZZZZ'), (1, 'ZZZ'), (2, 'ZZZ'), (2, 'ZZZZZ');
+
+SELECT id, MIN(s) FROM t1 GROUP BY id;
+
+DROP TABLE t1;
 # End of 4.1 tests

sql/item_sum.cc

@@ -930,7 +930,6 @@ Item_sum_hybrid::min_max_update_str_field()
 
   if (!args[0]->null_value)
   {
-    res_str->strip_sp();
     result_field->val_str(&tmp_value);
 
     if (result_field->is_null() ||