Key already in list error

https://github.com/martasp/BlazorLiveReload/blob/aab433f962187c78eb77c1f675be5b0efc7dc7f4/src/RazorComponentsPreview/Razor/TestRazorProjectFileSystem.cs#L29

Fix should be.
if (!_lookup.ContainsKey(item.CombinedPath))
            {
                _lookup.Add(item.FilePath, item);
            }