godoc: fix out-of-bounds panic when serving top-level files

Change-Id: I0ba84bac0c97715c0bc66fdc4c33678341ef140c
Reviewed-on: https://go-review.googlesource.com/53151
Reviewed-by: Chris Broadfoot <cbro@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/godoc/godoc_test.go b/godoc/godoc_test.go
index dca1c95..c1d631c 100644
--- a/godoc/godoc_test.go
+++ b/godoc/godoc_test.go
@@ -313,6 +313,8 @@
 	}{
 		{"src/", `<a href="/pkg">Index</a>`},
 		{"src/fmt/", `<a href="/pkg/fmt">fmt</a>`},
+		{"pkg/", `<a href="/pkg">Index</a>`},
+		{"pkg/LICENSE", `<a href="/pkg">Index</a>`},
 	} {
 		if got := srcToPkgLinkFunc(tc.path); got != tc.want {
 			t.Errorf("srcToPkgLinkFunc(%v) = %v; want %v", tc.path, got, tc.want)