Manually reverse 4377872, keeping stable tag and @stevenkword as a contributor.

See https://github.com/ethitter/WP-Print-Friendly/pull/4.
Braces make this massive conditional statement a skosh more legible to humans.
If WordPress determines the request is a 404, such as when a user who can't read a specific privately-published posts attempts to do so, prevent plugin from acting by setting `is_print()` to false.

See https://github.com/ethitter/WP-Print-Friendly/pull/4.