Paid multi-participant registration fails

Following on from #372 (closed) @mattwire

It is currently not possible to use Stripe payment gateway on a paid event which has 'multiple participants' enabled, where each participant adds a fee to the total.

Steps to recreate:

• Create an event
• Enable multiple participants, 1 additional guest
• Add a price to the event, and enable the stripe payment gateway
• Register for the event, and choose to bring a guest, ticking the fee in each case
• You are prompted for your card details on the 'first' page of registration
• Upon 'confirming' your registration, you are redirected back to the registration page, with the error: Stripe Property 'paymentIntentID' has not been set

Drupal 7, CiviCRM 5.52.2, Stripe 6.7.8, Payment shared 1.2.8