avcodec/indeo5: require initial valid intra/gop headers not just later

Fixes: Timeout
Fixes: 9308/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_INDEO5_fuzzer-5284853581873152

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

libavcodec/indeo5.c

@@ -642,6 +642,8 @@ static av_cold int decode_init(AVCodecContext *avctx)
     IVI45DecContext  *ctx = avctx->priv_data;
     int             result;
 
+    ctx->gop_invalid = 1;
+
     ff_ivi_init_static_vlc();
 
     /* copy rvmap tables in our context so we can apply changes to them */