Fix AttributeError on postcommit when db-create adds non-system CWSource entities In this case, `Repository.add_source` is called from an operation, not from `Repository.init_sources_from_database`, thus the attribute `sources_by_eid` does not exist. Closes #16251078.

Release notes
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.. toctree::
    :maxdepth: 1

    3.23
    3.22
    3.21
    3.20
    3.19
    3.18
    3.17
    3.16
    3.15
    3.14