filesystem: keep unmapped guest paths out of the host namespace

src/kernel/fileSystem.h

@@ -54,6 +54,7 @@ struct Lifecycle {
 
 void                  Mount(const std::filesystem::path& folder, const std::string& point);
 void                  Umount(const std::string& folder_or_point);
+// Returns an empty path when the guest path has no mounted filesystem.
 std::filesystem::path GetRealFilename(const std::string& mounted_file_name);
 
 int KYTY_SYSV_ABI     KernelOpen(const char* path, int flags, uint16_t mode);