Fix #11919: Typo prevents copying of users between projects

A typo introduced with the patch for issue #11530 prevented the copy
users from project A to project B feature from working.

Thanks to watergad for this patch.

manage_proj_user_copy.php

@@ -51,7 +51,7 @@
 	access_ensure_project_level( config_get( 'manage_project_threshold' ), $t_dst_project_id );
 	access_ensure_project_level( config_get( 'project_user_threshold' ), $t_dst_project_id );
 
-	project_copy_users( $t_dst_project_id, $t_src_project_id. access_get_project_level( $t_dst_project_id ) );
+	project_copy_users( $t_dst_project_id, $t_src_project_id, access_get_project_level( $t_dst_project_id ) );
 
 	form_security_purge( 'manage_proj_user_copy' );