Fix PHP warnings in print_code()

[damiencarbery]

$toolbar_height and $info_height use $font_size but that variable is a string with 'px !important;' at the end and so the multiplication causes php notices (PHP Notice: A non well formed numeric value encountered in /wp-content/plugins/crayon-syntax-highlighter/crayon_formatter.class.php on line 119). My code uses $_font_size which just contains a number.