Check for ~/ before using IOHelper.ResolveUrl

An "relative virtual path" exception can be thrown by a path like "umbraco/test.js"

src/Umbraco.Web/Editors/BackOfficeController.cs

@@ -475,7 +475,7 @@ namespace Umbraco.Web.Editors
                     if (isValid)
                     {
                         //it is a valid URL add to Url list
-                        urlList.Add(IOHelper.ResolveUrl(jsFile));
+                        urlList.Add(jsFile.StartsWith("~/") ? IOHelper.ResolveUrl(jsFile) : jsFile);
                     }
                 }
                 else