cdgraphics: do not rely on get_buffer() initializing the frame.

Setting it to zero (instead of 128, as the default get_buffer() does)
also produces more correctly-looking output.

cmdutils.c

@@ -1566,7 +1566,7 @@ static int alloc_buffer(FrameBuffer **pool, AVCodecContext *s, FrameBuffer **pbu
     /* XXX this shouldn't be needed, but some tests break without this line
      * those decoders are buggy and need to be fixed.
      * the following tests fail:
-     * cdgraphics, ansi, aasc, fraps-v1, qtrle-1bit
+     * ansi, aasc, fraps-v1, qtrle-1bit
      */
     memset(buf->base[0], 128, ret);
 

libavcodec/cdgraphics.c

@@ -287,6 +287,8 @@ static int cdg_decode_frame(AVCodecContext *avctx,
         av_log(avctx, AV_LOG_ERROR, "reget_buffer() failed\n");
         return ret;
     }
+    if (!avctx->frame_number)
+        memset(cc->frame.data[0], 0, cc->frame.linesize[0] * avctx->height);
 
     command = bytestream_get_byte(&buf);
     inst    = bytestream_get_byte(&buf);

tests/ref/fate/cdgraphics

@@ -1,20 +1,20 @@
 #tb 0: 1/300
-0,          0,          0,        1,   194400, 0xd919c635
-0,          1,          1,        1,   194400, 0xd919c635
-0,          2,          2,        1,   194400, 0x516a1007
-0,          3,          3,        1,   194400, 0x516a1007
-0,          4,          4,        1,   194400, 0x516a1007
-0,          5,          5,        1,   194400, 0x516a1007
-0,          6,          6,        1,   194400, 0x516a1007
-0,          7,          7,        1,   194400, 0x516a1007
-0,          8,          8,        1,   194400, 0x516a1007
-0,          9,          9,        1,   194400, 0x516a1007
-0,         10,         10,        1,   194400, 0x516a1007
-0,         11,         11,        1,   194400, 0x516a1007
-0,         12,         12,        1,   194400, 0x516a1007
-0,         13,         13,        1,   194400, 0x516a1007
-0,         14,         14,        1,   194400, 0x516a1007
-0,         15,         15,        1,   194400, 0x516a1007
+0,          0,          0,        1,   194400, 0x46ad80da
+0,          1,          1,        1,   194400, 0x46ad80da
+0,          2,          2,        1,   194400, 0x9392c3b9
+0,          3,          3,        1,   194400, 0x9392c3b9
+0,          4,          4,        1,   194400, 0x9392c3b9
+0,          5,          5,        1,   194400, 0x9392c3b9
+0,          6,          6,        1,   194400, 0x9392c3b9
+0,          7,          7,        1,   194400, 0x9392c3b9
+0,          8,          8,        1,   194400, 0x9392c3b9
+0,          9,          9,        1,   194400, 0x9392c3b9
+0,         10,         10,        1,   194400, 0x9392c3b9
+0,         11,         11,        1,   194400, 0x9392c3b9
+0,         12,         12,        1,   194400, 0x9392c3b9
+0,         13,         13,        1,   194400, 0x9392c3b9
+0,         14,         14,        1,   194400, 0x9392c3b9
+0,         15,         15,        1,   194400, 0x9392c3b9
 0,         16,         16,        1,   194400, 0x46ad80da
 0,         17,         17,        1,   194400, 0x46ad80da
 0,         18,         18,        1,   194400, 0x46ad80da