Helper for seek calls
Result is guaranteed to be positive.
EOVERFLOW returned if the arguments would cause an overflow.
EINVAL returned if the new offset is out of bounds.
Helper for seek calls
In most cases it’s easier to use a usize to track the offset and buffer size internally,
but the seek interface uses isize. This wrapper ensures EOVERFLOW errors are returned
as appropriate if the value in the usize can’t fit in the isize.