Fix dot path parsing on Windows

[djdv]

Follow up to PR #2135.
When trying to add dot (current working directory) the input path was not previously standardized to forward slashes which would cause malformed directory listings like those in issue #1922.
This commit should sanitize the path in the same way it is done at other entry points in the parser and force the path to use forward slashes instead of the FS native delimiter.

Possibly related to issue #1691.

[djdv]

It's worth noting the same result can be achieved by simply moving fpath = filepath.ToSlash(filepath.Clean(fpath)) down below the if block instead of doing the same conversion again inside the block, however fpath is evaluated in that if, as such I'm unsure which method would be preferable.

[whyrusleeping]

@djdv i think youre right on that, moving the cleanup to after the if seems like the right thing to do

[djdv]

@whyrusleeping
Understood, the commit has been changed and should be good.
Edit: Small newline infraction; amended.

[whyrusleeping]

@djdv thanks!