fix notices

Hi!

I use WordPress 4.0 and 4.1-alpha.
Version WP-Optimize 1.8.9.7

define( 'WP_DEBUG', true );

Found some notices
Undefined index: clean-revisions /wp-optimize/wp-optimize-main.php:15
Undefined index: clean-autodraft /wp-optimize/wp-optimize-main.php:30
Undefined index: clean-comments	/wp-optimize/wp-optimize-main.php:40
Undefined index: unapproved-comments /wp-optimize/wp-optimize-main.php:51
Undefined index: optimize-db /wp-optimize/wp-optimize-main.php:80