MDEV-27235: Crash on SET GLOBAL innodb_encrypt_tables

fil_crypt_set_encrypt_tables(): If no encryption threads have been
initialized, do nothing.

mysql-test/suite/innodb/r/temporary_table.result

@@ -136,6 +136,7 @@ show tables;
 Tables_in_test
 create temporary table t1 (keyc int, c1 char(100), c2 char(100)) engine = innodb;
 ERROR HY000: Can't create table `test`.`t1` (errno: 165 "Table is read only")
+SET GLOBAL innodb_encrypt_tables=DEFAULT;
 # test various bad start-up parameters
 FOUND 2 /InnoDB: Unable to create temporary file/ in mysqld.1.err
 FOUND 1 /innodb_temporary and innodb_system file names seem to be the same/ in mysqld.1.err

mysql-test/suite/innodb/t/temporary_table.test

@@ -121,6 +121,8 @@ show tables;
 --error ER_CANT_CREATE_TABLE
 create temporary table t1 (keyc int, c1 char(100), c2 char(100)) engine = innodb;
 
+SET GLOBAL innodb_encrypt_tables=DEFAULT;
+
 --echo # test various bad start-up parameters
 
 let SEARCH_FILE = $MYSQLTEST_VARDIR/log/mysqld.1.err;

storage/innobase/fil/fil0crypt.cc

@@ -2470,6 +2470,10 @@ void
 fil_crypt_set_encrypt_tables(
 	uint val)
 {
+	if (!fil_crypt_threads_inited) {
+		return;
+	}
+
 	mutex_enter(&fil_system->mutex);
 
 	srv_encrypt_tables = val;