swancustomenvironments: Avoid the use of ../ on the specified file value

Author: rodrigo-sobral

SwanCustomEnvironments/swancustomenvironments/templates/customenvs.html

@@ -71,7 +71,7 @@
     let has_failed = false, project_path = '/';
 
     const urlParams = new URLSearchParams(window.location.search);
-    const file = `/${urlParams.get('file') || ""}`;
+    const file = `/${urlParams.get('file') || ""}`.replace(/\.\.\//g, '').replace(/\.\.\\/g, '');
 
     // Scroll to the output-box height
     outputBox.scrollIntoView({