MDEV-32308 Server crash on cleanup of non-fully-constructed-due-to-an-error CTE

Cleanup sequence comes after error state when not all units were prepared.

The With_element without rec_result was created for following unit:
"select 1 AS `1` union select 'x' AS x from x" the error happened
in select "select x AS x" so above unit was not prepared. The case
seems to be legal and the presence of rec_result must be checked during
the cleanup.

mysql-test/main/cte_recursive.result

@@ -5857,3 +5857,10 @@ b	rank() over (order by c)
 drop view v1;
 drop table t1;
 # End of 10.4 tests
+#
+# MDEV-32308: Server crash on cleanup of
+# non-fully-constructed-due-to-an-error CTE
+#
+SELECT ( WITH RECURSIVE x AS ( WITH x AS ( SELECT 1 FROM t14 ) SELECT x ) , t14 AS ( SELECT 1 UNION SELECT 'x' FROM x ) SELECT x FROM x WHERE ( SELECT x FROM x ) ) ;
+ERROR 42S22: Unknown column 'x' in 'SELECT'
+# End of 10.6 tests

mysql-test/main/cte_recursive.test

@@ -4056,3 +4056,12 @@ drop view v1;
 drop table t1;
 
 --echo # End of 10.4 tests
+
+--echo #
+--echo # MDEV-32308: Server crash on cleanup of
+--echo # non-fully-constructed-due-to-an-error CTE
+--echo #
+--error ER_BAD_FIELD_ERROR
+SELECT ( WITH RECURSIVE x AS ( WITH x AS ( SELECT 1 FROM t14 ) SELECT x ) , t14 AS ( SELECT 1 UNION SELECT 'x' FROM x ) SELECT x FROM x WHERE ( SELECT x FROM x ) ) ;
+
+--echo # End of 10.6 tests

sql/sql_union.cc

@@ -2622,7 +2622,8 @@ bool st_select_lex_unit::cleanup()
       With_element *with_elem= with_element;
       while ((with_elem= with_elem->get_next_mutually_recursive()) !=
              with_element)
-        with_elem->rec_result->cleanup_count++;
+        if (with_elem->rec_result)
+          with_elem->rec_result->cleanup_count++;
       DBUG_RETURN(FALSE);
     }
   }