[Cache] Offer ids not correctly added to product page availability block identities

[rbayet]

Private method \Smile\RetailerOffer\Block\Catalog\Product\Retailer\Availability::getStoreOffers is called twice when displaying the availability block :

• once to initialize the JS component
• a second time to provide identities for the block

Unfortunately, the second time, the list of offers stored in $this->storeOffers is reset to an empty array.

This means that the block/page cache might not be cleared when a listed offer changes (availability, price or stock change).