fix: use the previous EV state when a blank state is received from the server (#207)

[rappazzo]

Maintain the previous vehicle state as a class variable on Vehicle.

[fuatakgun]

btw, thank you for raising this PR

[cdnninja]

Closing as this has aged out and V2 this would be a quick fix. Please raise a PR here if interested: https://github.com/Hyundai-Kia-Connect/hyundai_kia_connect_api

Would think a quick if statement on the value in the API would work in the new model.