Syntax improvements to prevent E_NOTICE/E_DEPRECATED errors.

• 672bef5: If a WordPress installation has WP_DEBUG=true, or has very low error_reporting, a 'Deprecated' notice is displayed. As of PHP 5.1 RC5 array and string offset access syntax with curly braces has been deprecated.
• efbbe72: If a WordPress installation has WP_DEBUG=true, or has a very low (notice) error_reporting threshold, [5] will raise a 'Notice: Undefined offset: 5' notice. Resolving this by using isset to test if offset 5 exists.