Fix null check in ContentAnchorTag

[hishamco]

This PR fixes a null check in

if (metadata.CreateRouteValues == null) // BUG
    {
      if (routeValues != null)
      {
        foreach (var attribute in routeValues)
        {
          metadata.CreateRouteValues.Add(attribute.Key, attribute.Value);     
        }
      }
      ....
    }

Also I did a little refactoring