tools/target_dec_fuzzer: Increase maxpixels threshold for dirac

wavelets allow significant size expansion and they are also not
very fast.

Fixes: Timeout
Fixes: 16480/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DIRAC_fuzzer-5659892689403904 (108sec -> 17ms)
Fixes: 16480/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DIRAC_fuzzer-5749422717140992 (big ->15sec)

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegReviewed-by: Tomas Härdin <tjoppen@acc.umu.se>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

tools/target_dec_fuzzer.c

@@ -128,6 +128,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     maxpixels = maxpixels_per_frame * maxiteration;
     switch (c->id) {
         // Allows a small input to generate gigantic output
+    case AV_CODEC_ID_DIRAC:     maxpixels /= 8192; break;
     case AV_CODEC_ID_MSRLE:     maxpixels /= 16;  break;
     case AV_CODEC_ID_QTRLE:     maxpixels /= 16;  break;
     case AV_CODEC_ID_GIF:       maxpixels /= 16;  break;