avcodec/rawdec: Free bitstream_buf

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
(cherry picked from commit 5c0f6d53da)

libavcodec/rawdec.c

@@ -493,6 +493,7 @@ static av_cold int raw_close_decoder(AVCodecContext *avctx)
     RawVideoContext *context = avctx->priv_data;
 
     av_buffer_unref(&context->palette);
+    av_freep(&context->bitstream_buf);
     return 0;
 }