Settings: Fix Uncaught TypeError

[n7studios]

Summary

Fixes this reported issue where clicking Save Changes on the settings screen results in an uncaughty TypeError when a Kit account has no resources, and no checkboxes are checked.

Testing

• testSettingsScreenWhenNoResources: Updated test to save all settings when the Kit account has no resources and no checkboxes are checked on the settings screen.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)