Assertion failure on empty pickling key in the keychain

[KitsuneRal]

As reported in the NeoChat room, an invalid (in that particular case, empty) pickling key in the keychain causes the library to fail an assertion, with the client code having no means to help that. With no good way out, perhaps it's best to fail the connection entirely and ask the user to remove/recover the pickling key, to avoid overwriting the database.