Accounts for the lazy initalization of availableStreamId array and fixes...

... the following exception

TypeError: Cannot read property 'length' of undefined
    at Connection.getInFlight (/Users/kfotev/Work/PierBelt/Wordpress/crawler-lite/node_modules/cassandra-driver/lib/connection.js:366:66)
    at /Users/kfotev/Work/PierBelt/Wordpress/crawler-lite/node_modules/cassandra-driver/lib/utils.js:178:24
    at Array.sort (native)
    at getLeastBusy (/Users/kfotev/Work/PierBelt/Wordpress/crawler-lite/node_modules/cassandra-driver/lib/host.js:116:24)
    at fn (/Users/kfotev/Work/PierBelt/Wordpress/crawler-lite/node_modules/cassandra-driver/node_modules/async/lib/async.js:641:34)
    at Object._onImmediate (/Users/kfotev/Work/PierBelt/Wordpress/crawler-lite/node_modules/cassandra-driver/node_modules/async/lib/async.js:557:34)
    at processImmediate [as _immediateCallback] (timers.js:345:15)