Handle npe's when loading the shopping cart (APPS-1779)

[Fabtron]

When loading the shopping cart some exception have not be handled leading to a npe. To handle this we now catch runtime exceptions to handle if the loading fails and create a new empty shopping cart.
We also only init the shopping cart with data if the data is not null to avoid npe's later on.

APPS-1779

How to test?

Definition of Done

• Issue is linked
• All requirements of the issue are fulfilled
• Changelog is updated
• Documentation is updated
• Self-Review
• Review with the Product Owner (Release-Variante o. Minified Build)

App Tests

• Minified build has been tested (aka. Release Build)
• Environments have been taken care of (Production/Staging)
• Supported languages have been tested
• Light-/Dark-Mode has been tested
• Edge-Cases have been tested
• Android API Levels have been taken care of (minSdk?)

Testing

• Tests have been written (aka Unit-Tests, Integration-Tests, ...)