Building dynamic biosphere fails if same code exists more than once in databases

[TimoDiepers]

Here, we have to come up with a more robust way of getting the "original biosphere flows".

https://github.com/brightway-lca/bw_timex/blob/de4b79bcd0b903efd2a6fd255478eed5f8c65480/bw_timex/dynamic_biosphere_builder.py#L160-L163