Handle invalid components.yaml file

[mixxorz]

Slippers should not crash if the contents of components.yaml isn't in the expected format.

It should show a helpful error message instead.

[ddahan]

More, it seems very weird that an empty components.yaml file lead to a AttributeError: 'NoneType' object has no attribute 'get' error, when running server. For me, an empty components.yaml file, or empty components list should not raise an error.