avcodec/rscc: Avoid returning frames that have nearly no undamaged pixels in them

Fixes: Timeout
Fixes: 12192/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RSCC_fuzzer-6279038004363264

Before: clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RSCC_fuzzer-6279038004363264 in 15423 ms
After:  clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RSCC_fuzzer-6279038004363264 in 190 ms

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

libavcodec/rscc.c

@@ -64,6 +64,7 @@ typedef struct RsccContext {
     /* zlib interaction */
     uint8_t *inflated_buf;
     uLongf inflated_size;
+    int valid_pixels
 } RsccContext;
 
 static av_cold int rscc_init(AVCodecContext *avctx)
@@ -347,8 +348,11 @@ static int rscc_decode_frame(AVCodecContext *avctx, void *data,
         }
         memcpy (frame->data[1], ctx->palette, AVPALETTE_SIZE);
     }
-
-    *got_frame = 1;
+    // We only return a picture when enough of it is undamaged, this avoids copying nearly broken frames around
+    if (ctx->valid_pixels < ctx->inflated_size)
+        ctx->valid_pixels += pixel_size;
+    if (ctx->valid_pixels >= ctx->inflated_size * (100 - avctx->discard_damaged_percentage) / 100)
+        *got_frame = 1;
 
     ret = avpkt->size;
 end: