don't alloc/free NULL

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@5470 b3059339-0415-0410-9bf9-f77b7e298cf2

libmpdemux/demuxer.c

@@ -347,7 +347,7 @@ void ds_free_packs(demux_stream_t *ds){
   demux_packet_t *dp=ds->first;
   while(dp){
     demux_packet_t *dn=dp->next;
-    free(dp->buffer);
+    if(dp->buffer) free(dp->buffer);
     free(dp);
     dp=dn;
   }

libmpdemux/demuxer.h

@@ -118,7 +118,7 @@ typedef struct demuxer_st {
 inline static demux_packet_t* new_demux_packet(int len){
   demux_packet_t* dp=malloc(sizeof(demux_packet_t));
   dp->len=len;
-  dp->buffer=malloc(len);
+  dp->buffer=len?malloc(len):NULL;
   dp->next=NULL;
   dp->pts=0;
   dp->pos=0;