Add outbound audio from PBX after answer

Seen on a few systems where due to firewall/nat configuration, there is no inbound RTP audio on SIP calls until AFTER RTP audio starts going out from the PBX. However in the case of outbound broadcast calls, there is no outbound audio until after the call has gone through the AMD part of the dialplan. In cases where there is no inbound RTP, AMD hears no audio and ALWAYS flags the calls as machine. I have tested a very simple fix that appears to work, play 1 second of silence after the the channel is answered:

exten => s,n,Answer
exten => s,n,Playback(silence/1)
exten => s,n,Set(_STATE=answered)
exten => s,n,AGI(broadcast_log.php)
exten => s,n,AMD()

Marked as feature request, but probably affects enough users to be considered a bug.

edit - thinking about this further, this probably should be added as a user option that is disabled by default. Enabling it will always cause AMD to miss the first second of audio from the answering party which may have undesirable consequences.