File objects seekable returns False even though they are seekable and seek returns None

[mxmlnkn]

import ext4
f = open("tests/nested-tar-10M.ext4", 'rb')
v = ext4.Volume(f)
i = v.inode_at('/foo/fighter/ufo')
file = i.open()
print(file.read(3))  # b'iri'
print(file.seek(1))  # None
print(file.read(3))  # b'riy'
print(file.seekable())  # False

The reason for this is BlockIO inheriting from io.RawIOBase without overriding the seekable method, which by default is inherited from io.IOBase and returns False.

Second bug: As per definition of io.IOBase, seek should:

Change the stream position to the given byte offset, interpreted relative to the position indicated by whence, and return the new absolute position.

However, it returns None as shown above.

[mxmlnkn]

The same for readable, which returns False.

[Eeems]

I'd be happy to accept a PR to fix this, it should also add a simple check to test.py to ensure that this doesn't get broken in the future.

[mxmlnkn]

I have opened a PR.