smacker: remove unnecessary call to avctx->release_buffer in decode_frame()

The release_buffer was cleaning the provided frame, thus causing the
successive call to avctx->reget_buffer() to allocate a new frame.  In
case the returned frame was not the same one previously returned but a
new one with different data, it resulted in artifacts.
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>

libavcodec/smacker.c

@@ -360,8 +360,6 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *data_size, AVPac
 
     if(buf_size <= 769)
         return 0;
-    if(smk->pic.data[0])
-            avctx->release_buffer(avctx, &smk->pic);
 
     smk->pic.reference = 1;
     smk->pic.buffer_hints = FF_BUFFER_HINTS_VALID | FF_BUFFER_HINTS_PRESERVE | FF_BUFFER_HINTS_REUSABLE;