Case of failure to get file list in dir by readdir_multi_head(v1.95) bug

The problem commented on in #2612 does not seem to occur only when IAM role is specified. https://github.com/s3fs-fuse/s3fs-fuse/blob/v1.95/src/curl_multi.cpp#L168

Because of this bug, if an error(other than a 200 response) occurs in multiple head requests(in threads), that request will result in an error. For example, if there is even one object in a directory that cannot be read (ex. due to permissions or encryption), file listing will not be possible. It will look like this:

$ ls
ls: reading directory .: Operation not permitted

I will share this information for future support.