[GithubIssueBridge] Avoid warning on missing title or numberSome issue "comments" (e.g. changes in labels) lack a title, leading toan ugly PHP warning:```rssbridge.WARNING Attempt to read property "plaintext" on null at bridges/GithubIssueBridge.php line 165```This commit checks whether an element was found before accessing`plaintext` on it, avoiding this specific warning.Equally, the issue number is checked before access.