retrieveAll() never calls callback if there is zero messages

[sidorares]

Had to add this to work around:

    Client.prototype.retrieve = function(what, callback) {
       if (what.length === 0) {
               callback(null, []);
       }

is this behaviour intentional?

[agsh]

Done, please test it

[sidorares]

great, thanks @agsh
when this is going to be on npm?

[agsh]

Done

[sidorares]

thanks!