added chain ID

[mgiulini]

You are about to submit a new Pull Request. Before continuing make sure you read the contributing guidelines and that you comply with the following criteria:

• You have sticked to Python. Please talk to us before adding other programming languages to HADDOCK3
• Your PR is about CNS
• Your code is well documented: proper docstrings and explanatory comments for those tricky parts
• You structured the code into small functions as much as possible. You can use classes if there is a (state) purpose
• Your code follows our coding style
• You wrote tests for the new code
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• Your PR is about writing tests for already existing code

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Closes #792

[VGPReys]

Nice catch !