This allows rewinding a directory by specifying the cookie 0, after
already scrolling a directory. This allows zig and clang functionality
to work which expect this.
This also fixes the case where a directory was allowed to be seeked.
This is prohibited by the current version of wasi-testsuite.
Signed-off-by: Adrian Cole <adrian@tetrate.io>
Co-authored-by: Takeshi Yoneda <takeshi@tetrate.io>