MDEV-8644 Using a UDF in a virtual column causes a crash when stopping the server

first close all tables, then unload UDFs

mysql-test/r/udf_notembedded.result

+create function sequence returns integer soname "UDF_EXAMPLE_LIB";
+create table t1 (n int key not null auto_increment,  msg int as (sequence()) virtual);
+select * from t1;
+n	msg
+drop table t1;
+drop function sequence;

mysql-test/t/udf_notembedded.test

+--source include/not_embedded.inc
+--source include/have_udf.inc
+
+#
+# MDEV-8644 Using a UDF in a virtual column causes a crash when stopping the server
+#
+--replace_result $UDF_EXAMPLE_SO UDF_EXAMPLE_LIB
+eval create function sequence returns integer soname "$UDF_EXAMPLE_SO";
+create table t1 (n int key not null auto_increment,  msg int as (sequence()) virtual);
+select * from t1;
+source include/restart_mysqld.inc;
+drop table t1;
+drop function sequence;
+

sql/mysqld.cc

@@ -1813,9 +1813,9 @@ void clean_up(bool print_message)
   item_user_lock_free();
   lex_free();				/* Free some memory */
   item_create_cleanup();
-  udf_free();
   table_def_start_shutdown();
   plugin_shutdown();
+  udf_free();
   ha_end();
   if (tc_log)
     tc_log->close();