Export error when no voice lines are selected [dev]

[vrad-exe]

Exporting seems to cause a crash on the latest dev

  + Exception Group Traceback (most recent call last):
  |   File "trio\_core\_run.py", line 948, in __aexit__
  | trio.NonBaseMultiError: <MultiError: <MultiError: AttributeError("'NoneType' object has no attribute 'casefold'")>>
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "app\UI.py", line 734, in export_editoritems
    |   File "exporting\__init__.py", line 154, in export
    |   File "step_order.py", line 105, in run
    |   File "trio\_core\_run.py", line 948, in __aexit__
    | trio.NonBaseMultiError: <MultiError: AttributeError("'NoneType' object has no attribute 'casefold'")>
    +-+---------------- 1 ----------------
      | Exception Group Traceback (most recent call last):
      |   File "step_order.py", line 45, in wrapper
      |   File "trio\_core\_run.py", line 948, in __aexit__
      | trio.NonBaseMultiError: AttributeError("'NoneType' object has no attribute 'casefold'")
      +-+---------------- 1 ----------------
        | Traceback (most recent call last):
        |   File "exporting\quote_pack.py", line 22, in step_quote_pack
        |   File "packages\__init__.py", line 465, in obj_by_id
        | AttributeError: 'NoneType' object has no attribute 'casefold'
        +------------------------------------