MDEV-15208: server crashed, when using ORDER BY with window function and UNION

(Edits by SergeiP: fix encryption.tempfiles_encrypted, re-word comment)

Global ORDER BY clause of a UNION may not refer to 1) aggregate functions
or 2) window functions.  setup_order() checked for #1 but not for #2.

mysql-test/suite/encryption/r/tempfiles_encrypted.result

@@ -4236,6 +4236,14 @@ i	LAST_VALUE(COUNT(i)) OVER (PARTITION BY i ORDER BY j)
 4	2
 DROP TABLE t1;
 #
+# MDEV-15208: server crashed, when using ORDER BY with window function and UNION
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(1),(1),(1),(1),(2),(2),(2),(2),(2),(2);
+SELECT 1 UNION SELECT a FROM t1 ORDER BY (row_number() over ());
+ERROR HY000: Expression #1 of ORDER BY contains aggregate function and applies to a UNION
+DROP TABLE t1;
+#
 # End of 10.2 tests
 #
 #