TT#75352 don't attempt to send uninitialised packets

This can presumably happen when an encoder gets re-initialised due to an
SSRC table overflow, or when a passthrough encoder (e.g. G.729) returns
no data.

Possibly fixes #915

Change-Id: Ib351054b99754f46d0a8fb2d49629ce7c48dc964
(cherry picked from commit 11e2893c0ef8480630dc416c7df9deba5e15775c)

daemon/codec.c

@@ -1330,7 +1330,7 @@ static int __packet_encoded(encoder_t *enc, void *u1, void *u2) {
 		int ret = ch->handler->dest_pt.codec_def->packetizer(in_pkt,
 				ch->sample_buffer, &inout, enc);
 
-		if (G_UNLIKELY(ret == -1)) {
+		if (G_UNLIKELY(ret == -1 || enc->avpkt.pts == AV_NOPTS_VALUE)) {
 			// nothing
 			free(buf);
 			break;