Do not pass audio until the remote side has indicated they are providing early media, or if the channel has been answered.

(closes issue #11823)
Reported by: SDamm


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@112204 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -4378,6 +4378,11 @@ static struct ast_frame *sip_read(struct ast_channel *ast)
 		}
 	}
 
+	/* Only allow audio through if they sent progress with SDP, or if the channel is actually answered */
+	if (p->invitestate != INV_EARLY_MEDIA && ast->_state != AST_STATE_UP) {
+		fr = &ast_null_frame;
+	}
+
 	ast_mutex_unlock(&p->lock);
 	return fr;
 }