Fix add button enable/disable logic when answering enumerator questions

[jeffpw-goog]

Description

When filling out an enumerator question in an application, the Add button is supposed to be disabled if any of the entries are blank. This only worked for entries that were created in the current page load. If entries were saved and then the page was reloaded, they would no longer participate in the enable/disable logic. This fixes that inconsistency so if an existing entry is blanked out the add button will be disabled.

Checklist

General

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• Added the correct label: < feature | enhancement | bug | under-development | dependencies | infrastructure | ignore-for-release | database >
• Assigned to a specific person, civiform/developers, or a more specific round-robin list
• Added an additional reviewer from outside your organization as FYI (if the primary reviewer is in the same organization as you)
• Created unit and/or browser tests which fail without the change (if possible)
• Performed manual testing (Chrome and Firefox if it includes front-end changes)

Instructions for manual testing

Steps to reproduce are in #7317.

Issue(s) this completes

Fixes #7317