Hi,

I found a crash input using the op_msg_fuzzer. The POC (base64 form) is :

/8sAAJmZltPUBwAAJG9vCG9vb29vb29vb29v////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////9vbzlvb29vb29vb29v729vb29vusU7gwAA
AAAA3QcAAAH//0QkBgA= 

To reproduce: 

cat poc_base64 | base64 -d > poc
./op_msg_fuzzer ./poc

Tested on Ubuntu 22.04

I have a question abou the harness. In `op_msg_fuzzer_fixture.cpp`, the harness creates a `Msg` from the fuzzer provided buffer:

    int new_size = Size + sizeof(int);
    auto sb = SharedBuffer::allocate(new_size);
    memcpy(sb.get(), &new_size, sizeof(int));
    memcpy(sb.get() + sizeof(int), Data, Size);
    Message msg(std::move(sb)); 

It seems such a message is not always valid (cannot be sent to the server from the client) so it might be a false crash? If so, is there any way to filter out such false crashes? If not, should I report all the crash I find using the harness? I would like to contribute to improve the correctness and security of mongodb. Looking forwards to hearing back from you.