avformat/matroskadec: Use av_freep() to avoid leaving stale pointers in memory

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 6e70e4aca5)

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

libavformat/matroskadec.c

@@ -1078,7 +1078,7 @@ static void ebml_free(EbmlSyntax *syntax, void *data)
                 for (j = 0; j < list->nb_elem;
                      j++, ptr += syntax[i].list_elem_size)
                     ebml_free(syntax[i].def.n, ptr);
-                av_free(list->elem);
+                av_freep(&list->elem);
             } else
                 ebml_free(syntax[i].def.n, data_off);
         default:
@@ -2132,7 +2132,7 @@ static int matroska_deliver_packet(MatroskaDemuxContext *matroska,
 {
     if (matroska->num_packets > 0) {
         memcpy(pkt, matroska->packets[0], sizeof(AVPacket));
-        av_free(matroska->packets[0]);
+        av_freep(&matroska->packets[0]);
         if (matroska->num_packets > 1) {
             void *newpackets;
             memmove(&matroska->packets[0], &matroska->packets[1],
@@ -2163,7 +2163,7 @@ static void matroska_clear_queue(MatroskaDemuxContext *matroska)
         int n;
         for (n = 0; n < matroska->num_packets; n++) {
             av_free_packet(matroska->packets[n]);
-            av_free(matroska->packets[n]);
+            av_freep(&matroska->packets[n]);
         }
         av_freep(&matroska->packets);
         matroska->num_packets = 0;
@@ -2995,7 +2995,7 @@ static int matroska_read_close(AVFormatContext *s)
 
     for (n = 0; n < matroska->tracks.nb_elem; n++)
         if (tracks[n].type == MATROSKA_TRACK_TYPE_AUDIO)
-            av_free(tracks[n].audio.buf);
+            av_freep(&tracks[n].audio.buf);
     ebml_free(matroska_cluster, &matroska->current_cluster);
     ebml_free(matroska_segment, matroska);