plumbing: format, Handle case where fs.Join breaks with C: in Windows

Signed-off-by: Paulo Gomes <[e-mail]>

plumbing/format/gitattributes/dir.go

···
 
 import (
 	"os"
+	"path/filepath"
+	"strings"
 
 	"github.com/go-git/go-billy/v5"
 
···
 			continue
 		}
 
-		path := append(root, fi.Name())
+		p := fi.Name()
+
+		// Handles the case whereby just the volume name ("C:") is appended,
+		// to root. Change it to "C:\", which is better handled by fs.Join().
+		if filepath.VolumeName(p) != "" && !strings.HasSuffix(p, string(filepath.Separator)) {
+			p = p + string(filepath.Separator)
+		}
+		path := append(root, p)
 
 		dirAttributes, err := ReadAttributesFile(fs, path, gitattributesFile, false)
 		if err != nil {