Prevent OnMessage event from firing when message is empty

[gacardinal]

Many browsers / client side implementations of the WebSocket protocol send a frame with a null byte just before disconnecting, in that case, the user of the library should not receive an OnMessage event.

[gacardinal]

Also, the OnMessage event should not be invoked if the message is comprised only of a unicode control character, because it seems like some browsers like to not follow the WebSocket specification and send things like an ETX unicode character in a data frame when the socket closes

[shelbyyyyy]

@Gaboik Is this still relevant? If not, please delete/close the issue. :)