Fix nb_lines computation when multiple pages on nanos

[abonnaudet-ledger]

(cherry picked from commit c9417b6)

Changes include

• Bugfix (non-breaking change that solves an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Tests
• Documentation
• Other (for changes that might not fit in any category)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

@@               Coverage Diff               @@
##             API_LEVEL_20     #695   +/-   ##
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  Coverage                ?   60.54%           
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  Files                   ?       12           
  Lines                   ?     1726           
  Branches                ?        0           
===============================================
  Hits                    ?     1045           
  Misses                  ?      681           
  Partials                ?        0           

Flag	Coverage Δ
unittests	60.54% <ø> (?)

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