Extend not-in-scope error for when it might be an integer column

[MichaelChirico]

Closes #697

[codecov]

Codecov Report

Merging #3589 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3589      +/-   ##
==========================================
+ Coverage   97.63%   97.63%   +<.01%     
==========================================
  Files          66       66              
  Lines       12702    12705       +3     
==========================================
+ Hits        12401    12404       +3     
  Misses        301      301

Impacted Files	Coverage Δ
R/data.table.R	97.68% <100%> (ø)	⬆️

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[codecov]

Codecov Report

Merging #3589 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3589      +/-   ##
==========================================
+ Coverage   97.63%   97.63%   +<.01%     
==========================================
  Files          66       66              
  Lines       12702    12708       +6     
==========================================
+ Hits        12401    12407       +6     
  Misses        301      301

Impacted Files	Coverage Δ
R/data.table.R	97.68% <100%> (ø)	⬆️
src/froll.c	100% <0%> (ø)	⬆️
src/frolladaptive.c	100% <0%> (ø)	⬆️

---

Continue to review full report at Codecov.

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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