Fix SIGSEGV in xmpp_component (#126)

* SIGSEGV in xmpp_component example with Prosody #126

xmpp_transport.go

@@ -14,6 +14,7 @@ import (
 )
 
 // XMPPTransport implements the XMPP native TCP transport
+// The decoder is expected to be initialized after connecting to a server.
 type XMPPTransport struct {
 	openStatement string
 	Config        TransportConfiguration