Clear spell-checker if new lang has no dictionary

[imnasnainaec]

Fixes #3183

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This change is 

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 74.59%. Comparing base (9feb899) to head (9bb8425).
Report is 33 commits behind head on master.

Files with missing lines	Patch %	Lines
src/utilities/spellChecker.ts	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3185      +/-   ##
==========================================
- Coverage   74.61%   74.59%   -0.03%     
==========================================
  Files         279      279              
  Lines       10694    10697       +3     
  Branches     1288     1289       +1     
==========================================
  Hits         7979     7979              
- Misses       2351     2354       +3     
  Partials      364      364              

Flag	Coverage Δ
backend	83.79% <ø> (-0.09%)	⬇️
frontend	66.53% <50.00%> (+0.03%)	⬆️

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[jasonleenaylor]

Reviewed 2 of 2 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @imnasnainaec)