Disable Oauth check if oauth disabled (#32368)

Fix #32367

---------

Co-authored-by: Giteabot <teabot@gitea.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/auth/oauth2.go

@@ -27,10 +27,15 @@ var (
 
 // CheckOAuthAccessToken returns uid of user from oauth token
 func CheckOAuthAccessToken(ctx context.Context, accessToken string) int64 {
-	// JWT tokens require a "."
+	if !setting.OAuth2.Enabled {
+		return 0
+	}
+
+	// JWT tokens require a ".", if the token isn't like that, return early
 	if !strings.Contains(accessToken, ".") {
 		return 0
 	}
+
 	token, err := oauth2_provider.ParseToken(accessToken, oauth2_provider.DefaultSigningKey)
 	if err != nil {
 		log.Trace("oauth2.ParseToken: %v", err)