Fix to issue in categories in a post that will not save when no categori...

This issue and the solution was found by @ufoloko. 

1-. Create a post and then select just one category, no tags. 
2.- Edit the post and remove the only category, the edit is not saved. 
This is because in SP, you have a condition for the tags, in edition when you remove the only category, you will not have any tag, so, you will not enter in condition to delete current tags, so change is not saved. 

For more details visit the link below
http://dnnblog.codeplex.com/workitem/24023