pngdec: do not release buffer on failure instead report full progress

Should fix heap-use-after-free as reported by Address Sanitizer.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavcodec/pngdec.c

@@ -868,8 +868,8 @@ static int decode_frame(AVCodecContext *avctx,
     return ret;
  fail:
     av_dict_free(&metadata);
+    ff_thread_report_progress(&s->picture, INT_MAX, 0);
     ret = AVERROR_INVALIDDATA;
-    ff_thread_release_buffer(avctx, &s->picture);
     goto the_end;
 }