S3Utils.getS3PosixFileAttributes can return null permissions for directories

[NaamaGertel]

In line 100 of S3Utils.getS3PosixFileAttributes method, if attr.isDirectory() we don't initialize the permissions. This can throw NullPointerException for user that don't expect this.

https://github.com/Upplication/Amazon-S3-FileSystem-NIO2/blob/master/src/main/java/com/upplication/s3fs/util/S3Utils.java#L100

[NaamaGertel]

I suggested a solution for this:
#113