Fixes an issue with InvoiceItemTypes reported by Christian on dev ML following proposed Nicolas's solution. 
I did not get further enough to add missing labels, like InvoiceItemType.description.SINVOICE_HEAD_ADJ, etc.
So when missing the default English description set in data seed is used

git-svn-id: https://svn.apache.org/repos/asf/ofbiz/trunk@1527171 13f79535-47bb-0310-9956-ffa450edef68