Fix for undocumented netatmo data structure change

The last_data_store data structure is internal and unsupported by netatmo despite the fact that obviously it's valuable for the community and doesn't cost anything to netatmo when looking at various developers forum contributions.

They decide without any notice of a change in this structure (for the good) that will make the library fail to retrieve last data. This fix will restore the normal behavior.

It's nice to see that some old software design flaws start to be fixed…
Still some work pending :-)