Wrong result when appending to UNC paths with only the host name

[rikyoz]

Describe the bug

Appending to an UNC path with only the host name (e.g., \\server) doesn't append the preferred separator before the appended path.
If the UNC path contains share names (e.g., \\server\share), appending works fine.

To Reproduce

Code:

namespace fs = std::filesystem;
namespace gfs = ghc::filesystem;

std::cout << (fs::path{"\\\\server"} / "abc") << " vs " << (gfs::path{"\\\\server"} / "abc") << std::endl;

Output:

"\\\\server\\abc" vs "\\\\serverabc"

Expected behavior

When appending to the path, the preferred path separator should also be appended before the appended path (in the example, \\\\server\\abc).

Additional context

Godbolt