After 957bc1881e686f9714c4e6a01bf33535091f0e21, we no longer compute an
expected_size for directories. This has the upshot that when we compare
even an empty Range with the available size, we fail.
This brings back the previous behaviour, which was to succeed, but with
empty content. This also removes the "Accept-ranges: bytes" header,
which is nonsensical on directories.
Adds test 3016
Fixes#6845Closes#6846
