Fix issue #46

[pitkant]

Fixes latter part of the issue described in #46 by making subsetting of columns less rigid in case of different column names between different years. What prompted this change was that sairaanhoitop_code column is missing from the most recent year 2023, which caused the following error in convert_municipality_key_codes function:

muns1 <- geofi::get_municipalities(codes_as_character = TRUE, year = 2023)

Error in `muni_key[, width_2]`:
! Can't subset columns that don't exist.
✖ Column `sairaanhoitop_code` doesn't exist.

[codecov]

Codecov Report

Merging #47 (0d6c4c7) into master (4173fd0) will decrease coverage by 2.67%.
The diff coverage is 0.00%.

❗ Current head 0d6c4c7 differs from pull request most recent head 983b99c. Consider uploading reports for the commit 983b99c to get more accurate results

@@            Coverage Diff             @@
##           master      #47      +/-   ##
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- Coverage   58.21%   55.55%   -2.67%     
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  Files           9        9              
  Lines         146      153       +7     
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  Hits           85       85              
- Misses         61       68       +7     

Impacted Files	Coverage Δ
R/convert_codes_as_character.R	0.00% <0.00%> (ø)