fix: fix findCustomID to prevent early escape

[slavanossar]

What?

Don't return a truthy value for group-like fields and discontinue field traversal within the findCustomID callback function.

Why?

Currently, there is a bug that prevents customIDType being set correctly when the custom ID field is placed after a tabs field that includes a tab with a name, since the first condition will return true and prevent further field traversal. This bug only becomes apparent when using a number type for the custom ID field, since customIDType is undefined so the typing defaults to text (breaking field validation, as well as <Document> views where findByID is passed a string instead of a number)

Here's an example of a CollectionConfig that would be affected:

const MyCollection: CollectionConfig = {
  slug: 'myCollection',
  fields: [
    {
      type: 'tabs',
      tabs: [
        {
          label: 'Tab',
          fields: [
            // ...
          ]
        },
        {
          name: 'namespacedTab',
          fields: [
            // ...
          ]
        }
      ]
    },
    {
      name: 'id',
      type: 'number',
      required: true,
      unique: true,
      admin: {
        readOnly: true,
      }
    }
  ]
}

See this Discord thread for additional context.

How?

Just use an undefined return, like the subsequent check for fieldAffectsData.