Fails for products that are unavailable (i.e. out of stock)

[DanCousins]

Trying to monitor for iPhone 15 Pro Max, running into an error. Dug into it a little and it looks like it isn't supported for out of stock devices.

`[dan@fedora Apple-Store-Reserve-Monitor]$ python store_checker.py
➜ Downloading Models List...
✖ Failed to find the device family
➜ Looking for device models instead...
✔ Found 1 devices matching your config.
➜ Downloading Stock Information for the devices...

1/1 [▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉]Traceback (most recent call last):
File "/home/dan/python/Apple-Store-Reserve-Monitor/store_checker.py", line 242, in
store_checker.refresh()
File "/home/dan/python/Apple-Store-Reserve-Monitor/store_checker.py", line 83, in refresh
self.check_stores_for_device(device)
File "/home/dan/python/Apple-Store-Reserve-Monitor/store_checker.py", line 188, in check_stores_for_device
for store in store_list:
TypeError: 'NoneType' object is not iterable
`

Printing the content of "product_availability_response" from line 181 provides the following:

b'{"head":{"status":"200","data":{}},"body":{"overlayInitiatedFromWarmStart":false,"viewMoreHoursLinkText":"View more hours","little":false,"errorMessage":"Product(s) Invalid or not buyable","location":"REDACTED","notAvailableNearby":"Not available today at [X] nearest stores.","notAvailableNearOneStore":"Not available today at the nearest store.","warmDudeWithAPU":false,"viewMoreHoursVoText":"(opens in new window)","viewDetailsText":"View details","legendLabelText":"Stores","filteredTopStore":false}}