Added return value check
Added return value check

The openssl_random_pseudo_bytes function will return false on failure.
eXcomm/php-bitpay-client,samuelbohler/php-bitpay-client,Tetpay/php-bitpay-client,ionux/php-bitpay-client,ionux/php-bitpay-client,Tetpay/php-bitpay-client,Tetpay/php-bitpay-client,initaldk/php-bitpay-client,initaldk/php-bitpay-client,samuelbohler/php-bitpay-client,bitpay/php-bitpay-client,bitpay/php-bitpay-client,eXcomm/php-bitpay-client