ext: Fix panic when URL path is empty

middleware/extensions/ext.go

@@ -31,7 +31,7 @@ type Ext struct {
 // ServeHTTP implements the middleware.Handler interface.
 func (e Ext) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 	urlpath := strings.TrimSuffix(r.URL.Path, "/")
-	if path.Ext(urlpath) == "" && r.URL.Path[len(r.URL.Path)-1] != '/' {
+	if path.Ext(urlpath) == "" && len(r.URL.Path) > 0 && r.URL.Path[len(r.URL.Path)-1] != '/' {
 		for _, ext := range e.Extensions {
 			if resourceExists(e.Root, urlpath+ext) {
 				r.URL.Path = urlpath + ext

middleware/extensions/ext_test.go

@@ -30,6 +30,7 @@ func TestExtensions(t *testing.T) {
 		{"/extensions_test/", []string{".html"}, "/extensions_test/"},
 		{"/extensions_test", []string{".json"}, "/extensions_test"},
 		{"/another_test", []string{".html"}, "/another_test"},
+		{"", []string{".html"}, ""},
 	} {
 		ex := Ext{
 			Next: middleware.HandlerFunc(func(w http.ResponseWriter, r *http.Request) (int, error) {