`PhoneInput` edge case when input text is cleared

[Lordfirespeed]

Related: #1

Source: DurHack project (ducompsoc/durhack) 'contact' application form

To reproduce

1. Enter a valid phone number (e.g. +44 123456789)
2. Clear text
3. Start typing a new phone number with a different prefix (e.g. +61 ...)
4. Clear text

Actual result

The selected phone number prefix reverts to the prefix of the last 'valid' input text (+44)

Expected result

The selected phone number prefix should revert to 'indeterminate'

Notes

Problem could be related to usage via react-hook-form - passing in the value prop?