avcodec/vble: Allocate buffer later

Fixes: Timeout
Fixes: 71727/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VBLE_fuzzer-6126342574243840

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/vble.c

@@ -130,10 +130,6 @@ static int vble_decode_frame(AVCodecContext *avctx, AVFrame *pic,
         return AVERROR_INVALIDDATA;
     }
 
-    /* Allocate buffer */
-    if ((ret = ff_thread_get_buffer(avctx, pic, 0)) < 0)
-        return ret;
-
     /* Version should always be 1 */
     version = AV_RL32(src);
 
@@ -148,6 +144,10 @@ static int vble_decode_frame(AVCodecContext *avctx, AVFrame *pic,
         return AVERROR_INVALIDDATA;
     }
 
+    /* Allocate buffer */
+    if ((ret = ff_thread_get_buffer(avctx, pic, 0)) < 0)
+        return ret;
+
     /* Restore planes. Should be almost identical to Huffyuv's. */
     vble_restore_plane(ctx, pic, &gb, 0, offset, avctx->width, avctx->height);