6.8.4 clearErrors with nested fields + formState.isValid

[szymonlesisz]

Describe the bug
Calling clearErrors doesn't have affect on formState.isValid field

To Reproduce
Steps to reproduce the behavior:

1. Go to https://codesandbox.io/s/react-hook-form-useform-template-forked-j4wqk?file=/src/index.js
2. Click on 'Step 1'
3. Click on 'Step 2'
4. See console logs

There are two cases:

1. if setValue in "step 2" triggers validation (shouldValidate: true) errors object is empty
2. if setValue in "step 2" doesn't trigger validation errors object is not empty but got undefined values

In both cases formState.isValid is set to false

Expected behavior
formState.isValid should be set to true after "Step 2"