PLT-5702 Added special error page for private browsing error message (#5985)

webapp/utils/markdown.jsx

@@ -163,6 +163,10 @@ class MattermostMarkdownRenderer extends marked.Renderer {
     link(href, title, text) {
         let outHref = href;
 
+        if (this.formattingOptions.linkFilter && !this.formattingOptions.linkFilter(outHref)) {
+            return text;
+        }
+
         try {
             let unescaped = unescape(href);
             try {