Reduce memory usage in wp-includes/kses.php by switching unnecessary empty...

Reduce memory usage in wp-includes/kses.php by switching unnecessary empty arrays to boolean. Fixes #20017.

safecss_filter_attr() block for style tags must be moved out of the is_array() only branch of wp_kses_attr() to accommodate for this.


git-svn-id: https://core.svn.wordpress.org/trunk@19976 1a063a9b-81f0-0310-95a4-ce76da25c4cd