internal/fetch: skip over READMEs that are directories

Change-Id: I8b214e964a0d725c691ac46850ebf6da32451a26
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/345113
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>
diff --git a/internal/fetch/readme.go b/internal/fetch/readme.go
index a2da4e5..6649772 100644
--- a/internal/fetch/readme.go
+++ b/internal/fetch/readme.go
@@ -28,7 +28,7 @@
 		if err != nil {
 			return err
 		}
-		if isReadme(pathname) {
+		if !d.IsDir() && isReadme(pathname) {
 			info, err := d.Info()
 			if err != nil {
 				return err
diff --git a/internal/fetch/readme_test.go b/internal/fetch/readme_test.go
index 428cfa7..1593683 100644
--- a/internal/fetch/readme_test.go
+++ b/internal/fetch/readme_test.go
@@ -80,6 +80,14 @@
 			version:    "v1.0.0",
 			files:      map[string]string{},
 		},
+		{
+			name:       "readme is a directory",
+			modulePath: "github.com/my/module",
+			version:    "v1.0.0",
+			files: map[string]string{
+				"foo/README/bar": "README",
+			},
+		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			var (