fix messageSentHandlerBinary initilization

melody.go

@@ -44,6 +44,7 @@ func New() *Melody {
 		messageHandler:           func(*Session, []byte) {},
 		messageHandlerBinary:     func(*Session, []byte) {},
 		messageSentHandler:       func(*Session, []byte) {},
+		messageSentHandlerBinary: func(*Session, []byte) {},
 		errorHandler:             func(*Session, error) {},
 		connectHandler:           func(*Session) {},
 		disconnectHandler:        func(*Session) {},