Fix segfault on answer.

Only update/change RTP source if RTP has already been started and 
connected to the subchannel.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@348849 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_skinny.c

@@ -4812,10 +4812,14 @@ static int skinny_indicate(struct ast_channel *ast, int ind, const void *data, s
 	case AST_CONTROL_PROCEEDING:
 		break;
 	case AST_CONTROL_SRCUPDATE:
+		if (sub->rtp) {
 			ast_rtp_instance_update_source(sub->rtp);
+		}
 		break;
 	case AST_CONTROL_SRCCHANGE:
+		if (sub->rtp) {
 			ast_rtp_instance_change_source(sub->rtp);
+		}
 		break;
 	case AST_CONTROL_CONNECTED_LINE:
 		update_connectedline(sub, data, datalen);