Ensure random_bytes function is available when decrypting

PHP 7 introduced the random_bytes function, which is required by the Defuse PHP-Encryption library. To provide backward-compatibility with versions of PHP prior to 7.0, it is recommended that the random_compat PHP library is installed. Currently, Real AES only checks to make sure the random_bytes function is available during encryption. Defuse PHP-Encryption, however, verifies that the function exists during its environment check, which also takes place during decryption. Real AES needs to load the random_compat library during decryption for versions of PHP below 7.0.