tools/target_bsf_fuzzer: skip filters that av_bsf_alloc() does not support

This is not a security issue.

Fixes: 538624321/clusterfuzz-testcase-minimized-ffmpeg_BSF_LCEVC_MERGE_fuzzer-6371982149746688
Fixes: lrIny8K4GGmb

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

tools/target_bsf_fuzzer.c

@@ -60,6 +60,8 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     }
 
     res = f ? av_bsf_alloc(f, &bsf) : av_bsf_get_null_filter(&bsf);
+    if (res == AVERROR(ENOTSUP))
+        return 0; // multi-input filters cannot be used through av_bsf_alloc()
     if (res < 0)
         error("Failed memory allocation");
     f = bsf->filter;