Use deterministic assignments for unique_id
Use deterministic assignments for unique_id

Fixes qpdf/qpdf#419

qpdf/qpdf,qpdf/qpdf,jberkenbilt/qpdf,jberkenbilt/qpdf,jberkenbilt/qpdf,qpdf/qpdf,qpdf/qpdf,jberkenbilt/qpdf,qpdf/qpdf,jberkenbilt/qpdf