Bug: Search App: Variant Pricing become null when product/variant updated via webhook

[Sihana-Shybin]

### What are you trying to achieve?
I added a product and it's variants in Saleor and did the bulk indexing as well. If I am editing the product or variant, the pricing details in algolia such as price, discount, priceUndiscounted, onSale will become null. This is happening for delta indexed product and other products have the details as it was during full indexing. This is happening to all the indices corresponds to each channel where the product or variant is available.
The data getting from the webhook has pricing as null:

and in the index,

### Steps to reproduce the problem

1. Create a product and it's variants in algolia
2. Do full indexing from Saleor UI
3. Update a product or it's variant
4. Check whether it is updated in the index as well through delta indexing
5. The prooperty changed will be updated in index. However the pricing object in the variant will become empty

### What did you expect to happen?
The product variant pricing should not be null and it should be available in the index even after the delta indexing

I am using saleor-platform for setting up the saleor.

[freebreix]

Same as #1108