Set Pages dict Type if not set

[adrg]

Addresses #416

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (v3@ca4f19e). Click here to learn what that means.
The diff coverage is 0%.

@@          Coverage Diff          @@
##             v3     #419   +/-   ##
=====================================
  Coverage      ?   59.51%           
=====================================
  Files         ?      153           
  Lines         ?    27683           
  Branches      ?        0           
=====================================
  Hits          ?    16475           
  Misses        ?    10836           
  Partials      ?      372

Impacted Files	Coverage Δ
pdf/model/reader.go	65.43% <0%> (ø)

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