Cannot access S3 bucket root when the access policy checks for empty prefix

[martinprikryl]

When accessing bucket root, AWS tools send empty prefix (prefix=), contrary to libs3 that sends no prefix. But some AWS policy examples suggest conditions like: "Condition":{"StringEquals":{"s3:prefix":["","home/"],"s3:delimiter":["/"]}} With such conditions libs3 will fail to access the root. Reported for WinSCP: https://winscp.net/forum/viewtopic.php?t=31359 The same problem for Cyberduck: https://trac.cyberduck.io/ticket/11549