fix(documents): fix maxFileSize when it is loaded from g:coc_user_config

[dmitmel]

It was broken by the commit a4e83d1.

[codecov]

Codecov Report

Merging #3610 (e9ff84d) into master (c1a97aa) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3610      +/-   ##
==========================================
- Coverage   76.59%   76.55%   -0.05%     
==========================================
  Files         202      202              
  Lines       19977    19977              
  Branches     4446     4446              
==========================================
- Hits        15301    15293       -8     
- Misses       2925     2930       +5     
- Partials     1751     1754       +3     

Impacted Files	Coverage Δ
src/core/documents.ts	88.65% <100.00%> (-0.62%)	⬇️
src/model/status.ts	88.09% <0.00%> (-4.77%)	⬇️
src/extensions.ts	57.92% <0.00%> (-0.50%)	⬇️
src/completion/index.ts	76.20% <0.00%> (-0.25%)	⬇️
src/services.ts	22.75% <0.00%> (ø)

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