diracdec: check return code of get_buffer_with_edge

If it fails, buffers aren't allocated, causing NULL pointer dereferencing.
Reviewed-by: Rostislav Pehlivanov <atomnuker@gmail.com>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavcodec/diracdec.c

@@ -1975,7 +1975,9 @@ static int dirac_decode_picture_header(DiracContext *s)
             for (j = 0; j < MAX_FRAMES; j++)
                 if (!s->all_frames[j].avframe->data[0]) {
                     s->ref_pics[i] = &s->all_frames[j];
-                    get_buffer_with_edge(s->avctx, s->ref_pics[i]->avframe, AV_GET_BUFFER_FLAG_REF);
+                    ret = get_buffer_with_edge(s->avctx, s->ref_pics[i]->avframe, AV_GET_BUFFER_FLAG_REF);
+                    if (ret < 0)
+                        return ret;
                     break;
                 }