obu: free Metadata buffers at the start of a new Sequence

They only apply to the old one.

src/obu.c

@@ -1243,6 +1243,10 @@ int dav1d_parse_obus(Dav1dContext *const c, Dav1dData *const in, int global) {
             c->frame_hdr = NULL;
         else if (memcmp(seq_hdr, c->seq_hdr, sizeof(*seq_hdr))) {
             c->frame_hdr = NULL;
+            c->mastering_display = NULL;
+            c->content_light = NULL;
+            dav1d_ref_dec(&c->mastering_display_ref);
+            dav1d_ref_dec(&c->content_light_ref);
             for (int i = 0; i < 8; i++) {
                 if (c->refs[i].p.p.data[0])
                     dav1d_thread_picture_unref(&c->refs[i].p);