PingAgent ignores zero-data ping-packets

[Crokoking]

The websocket standard allows for ping-packets with no data. But since the PingAgent uses 0 to determine that it doesn't need to send a pong it essentially ignores it. There is a related issue that encodeData() in the FrameEncoder processes zero-length packets with zero frames and thereby ignores them.

[epickrram]

Hi, thanks for the report. We'll look at this when possible. In the mean time, feel free to submit a PR containing a fix.