rmdec: fix null derefercne

Fixes CID733714
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/rmdec.c

@@ -839,7 +839,8 @@ ff_rm_retrieve_cache (AVFormatContext *s, AVIOContext *pb,
         ast->deint_id == DEINT_ID_VBRS)
         av_get_packet(pb, pkt, ast->sub_packet_lengths[ast->sub_packet_cnt - rm->audio_pkt_cnt]);
     else {
-        av_new_packet(pkt, st->codec->block_align);
+        if(av_new_packet(pkt, st->codec->block_align) < 0)
+            return AVERROR(ENOMEM);
         memcpy(pkt->data, ast->pkt.data + st->codec->block_align * //FIXME avoid this
                (ast->sub_packet_h * ast->audio_framesize / st->codec->block_align - rm->audio_pkt_cnt),
                st->codec->block_align);
@@ -867,7 +868,9 @@ static int rm_read_packet(AVFormatContext *s, AVPacket *pkt)
         if (rm->audio_pkt_cnt) {
             // If there are queued audio packet return them first
             st = s->streams[rm->audio_stream_num];
-            ff_rm_retrieve_cache(s, s->pb, st, st->priv_data, pkt);
+            res = ff_rm_retrieve_cache(s, s->pb, st, st->priv_data, pkt);
+            if(res < 0)
+                return res;
             flags = 0;
         } else {
             if (rm->old_format) {