When flagrow.io runs into an exception, we simply get an empty list of extensions

[clarkwinkelmann]

The reason is that data defaults to [] in ExtensionRepository and we never check the http code.

Expected behaviour:

The Bazaar UI displays an error and don't cache the result

Actual behaviour:

The 500 errors are cached and the UI simply displays an empty list of extension.

[luceos]

We should at least test the status code returned..