tools/target_dec_fuzzer: adjust pixel threshold for MSRLE, as it allows coding gigantic images on tiny input

Fixes: Timeout (12sec ->2sec)
Fixes: 16125/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MSRLE_fuzzer-5650846364205056

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

tools/target_dec_fuzzer.c

@@ -170,6 +170,7 @@ 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_MSRLE:     maxpixels /= 16;  break;
     case AV_CODEC_ID_QTRLE:     maxpixels /= 16;  break;
     case AV_CODEC_ID_GIF:       maxpixels /= 16;  break;
         // Performs slow frame rescaling in C