fix issue 407, where if server URL has no path it throws exception (#408

)

Co-authored-by: Naer Chang <naer_chang@mcafee.com>

routers/gorillamux/router.go

@@ -43,7 +43,7 @@ func NewRouter(doc *openapi3.T) (routers.Router, error) {
 			return nil, err
 		}
 		path := bDecode(u.EscapedPath())
-		if path[len(path)-1] == '/' {
+		if len(path) > 0 && path[len(path)-1] == '/' {
 			path = path[:len(path)-1]
 		}
 		servers = append(servers, srv{

routers/gorillamux/router_test.go

@@ -206,3 +206,16 @@ func TestPermuteScheme(t *testing.T) {
 	perms := permutePart(scheme0, server)
 	require.Equal(t, []string{"http", "https"}, perms)
 }
+
+func TestServerPath(t *testing.T) {
+	server := &openapi3.Server{URL: "http://example.com"}
+	err := server.Validate(context.Background())
+	require.NoError(t, err)
+
+	_, err = NewRouter(&openapi3.T{Servers: openapi3.Servers{
+		server,
+		&openapi3.Server{URL: "http://example.com/"},
+		&openapi3.Server{URL: "http://example.com/path"}},
+	})
+	require.NoError(t, err)
+}