Fix signaling onMessage when endpointId is missing
Fix signaling onMessage when endpointId is missing

This can currently happen if the server posts a message directly to an
endpoint.

Signed-off-by: Chad McElligott <88e591b29ffc678e41955e2dbb51051ae8c9ec04@digium.com>

respoke/respoke,respoke/respoke,respoke/respoke