PHPC-1629: Check if read preference is valid during unserialization
PHPC-1629: Check if read preference is valid during unserialization

jmikola/mongo-php-driver,jmikola/mongo-php-driver,mongodb-labs/mongo-php-driver-prototype,mongodb-labs/mongo-php-driver-prototype,jmikola/mongo-php-driver-prototype,jmikola/mongo-php-driver-prototype,jmikola/mongo-php-driver-prototype,jmikola/mongo-php-driver,mongodb/mongo-php-driver,mongodb/mongo-php-driver,jmikola/mongo-php-driver-prototype,mongodb/mongo-php-driver,jmikola/mongo-php-driver,jmikola/mongo-php-driver,mongodb/mongo-php-driver,mongodb-labs/mongo-php-driver-prototype,jmikola/mongo-php-driver-prototype,mongodb-labs/mongo-php-driver-prototype,mongodb-labs/mongo-php-driver-prototype,mongodb/mongo-php-driver