Terms list table shouldn't display if no terms

[westi]

If no terms exist in a taxonomy then we should display a message instead of an empty table.

It seems like we should fetch the terms in prepare_items to do this as otherwise the has_items stuff just doesn't work :-(

A starter for one

As you can see from the patch I started trying to implement this the same way the posts one worked and then found that I couldn't because we don't fetch the terms until we are displaying the table :-(

Actually, the current behaviour is consistent with the 3.0 branch.

It's this way because the "Add new term" form on the left automatically populates the table on the right.