Fixes #16

Fix by @bobrik

lib/apn.js

@@ -48,7 +48,7 @@ var Connection = function (optionArgs) {
 	}
 
 	var onDrain = function() {
-		if (writeBuffer.length) {
+		while (writeBuffer.length && self.socket.bufferSize == 0) {
 			writeNotificationToSocket(writeBuffer.shift());
 		}
 	};