Answerd an editor corner case.

You can now type (wa 1 1) and nothing blows up.

The screen simply redraws.

Example:

    Abjad IDE - scores - views (EDIT)

       1: bača: not md:is_example
       2: examples: md:is_example

          elements - add (add)
          elements - remove (rm)
          elements - rename (ren)
          editing - done (done)

    |> 1

    Abjad IDE - scores - views - bača (EDIT)

       1: not md:is_example

          elements - add (add)
          elements - remove (rm)
          editing - done (done)

    |> 1

    Abjad IDE - scores - views - bača (EDIT)

       1: not md:is_example

          elements - add (add)
          elements - remove (rm)
          editing - done (done)

    |>

Did this by teaching CollectionAutoeditor.edit_item() not to freak out when the
item-to-be-edited has not _attribute_manifest property.