Codechange: use std::string for FiosIsRoot

src/os/windows/win32.cpp

@@ -168,9 +168,9 @@ int closedir(DIR *d)
 	return 0;
 }
 
-bool FiosIsRoot(const char *file)
+bool FiosIsRoot(const std::string &file)
 {
-	return file[3] == '\0'; // C:\...
+	return file.size() == 3; // C:\...
 }
 
 void FiosGetDrives(FileList &file_list)