MDEV-19914 Server startup fails while dropping garbage encrypted tablespace if...

MDEV-19914 Server startup fails while dropping garbage encrypted tablespace if innodb_encryption_threads > 0

- Avoiding accessing encryption thread mutex before initiating
the encryption threads

mysql-test/suite/encryption/t/innodb-encryption-alter.test

@@ -123,6 +123,7 @@ SET DEBUG_SYNC = 'now WAIT_FOR done';
 SET GLOBAL innodb_flush_log_at_trx_commit=1;
 COMMIT;
 
+let $restart_parameters = --innodb_encryption_threads=2;
 --let $shutdown_timeout= 0
 --source include/restart_mysqld.inc
 disconnect con1;

storage/innobase/fil/fil0crypt.cc

@@ -2414,7 +2414,8 @@ fil_space_crypt_close_tablespace(
 {
 	fil_space_crypt_t* crypt_data = space->crypt_data;
 
-	if (!crypt_data || srv_n_fil_crypt_threads == 0) {
+	if (!crypt_data || srv_n_fil_crypt_threads == 0
+	    || !fil_crypt_threads_inited) {
 		return;
 	}