LP#1830394: remove console noise from the holdings editor

LP#1830394: remove console noise from the holdings editor

This patch removes browser console noise that occurs (among other
places) when moving a working item to the completed list in
the holdings editor

TypeError: "$scope.working.MultiMap[keys[i]] is undefined"
    hasMulti https://evergreen.example.org/js/ui/default/staff/cat/volcopy/app.js:1203
    ...

To test
-------
[1] Open the holdings editor to add or edit an item, then open the
    browser debug console.
[2] Make a change and move the item from working to complete. Note
    that the error message above shows up repeated in the
    console log.
[3] Apply the patch and repeat steps 1 and 2. This time, the errors
    should not appear.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>