fix: handle Windows drive root paths (C:/) in shared directories to prevent 0 files shown

[jolavillette]

Problem

On Windows, sharing a drive at its root level (e.g. [C:/] or [D:/]) results in RetroShare displaying 0 shared files. This is a regression introduced by the recent fix for _wstat failing on trailing slashes in [checkDirectory()]

Root cause

Three interacting issues:

1. [checkDirectory()] — The trailing slash stripping turns [C:/] into [C:], which under Windows API (_wstat) refers to the current working directory on drive C, not the drive root. These are two fundamentally different concepts inherited from DOS.

2. FolderIterator::updateFileInfo() — The path construction mFolderName + "/" + mFileName produces double slashes (C://file) when iterating a drive root, causing _wstati64 to fail silently on each entry.

3. [recursUpdateSharedDir()] — Same double-slash issue in 3 manual path concatenations (cumulated_path + "/" + name).

Fix

• After stripping trailing slashes, restore \ if the result is a bare drive letter ([C:] → C:\)
• Check if path already ends with a separator before adding one in FolderIterator
• Replace 3 manual concatenations with RsDirUtil::makePath() which already handles trailing separators correctly

[csoler]

why don' tyou use RsDirUtil::makePath() here as well?

[jolavillette]

done