Update field in a no-fallback form with array value should not create fields for the array items

[riceyeh]

Hi,
The following test shows fields for array items are created when update a field in a no-fallback form with array value:

`
describe.only('no fallback', () => {
it('no new field for array value', () => {
const fields = ['prop']
const values = {
prop: [1, 2, 3]
}
const form = new Form({fields, values}, {name: 'Form without fallback', options: {fallback: false}})

	expect(form.select('prop.0',undefined, false)).to.be.undefined // <--- fail

	expect(form.$('prop').value).to.deep.equal([1, 2, 3])
	form.update({prop: [4, 5, 6]})
	expect(form.select('prop.0', undefined, false)).to.be.undefined
	expect(form.$('prop').value).to.deep.equal([4, 5, 6])
})

})
`