Don't crash when snaks-order is missing in API result

On older Wikibase versions, snaks-order is not returned from the API results for the items.
If this is the case, the bot crashes when it gets the data.
This fix ensures compatibility with those older version of Wikibase.

Bug: T76833
Change-Id: Ic014c682443919017eb9cd57b883511a6189af91