Fixed: Use the modified post date if the creation date is empty
Fixed: Warning: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object


git-svn-id: https://plugins.svn.wordpress.org/fg-joomla-to-wordpress/trunk@779407 b8457f37-d9ea-0310-8a92-e5e31aec5664