[spiral/translator] Add a check for the existence of a message

[msmakouz]

Q	A
Bugfix?	✔️
Breaks BC?	❌
New feature?	❌
Issues	#1060

The code did not check whether the message already exists (loaded from the translation files). A check for the existence of the message in the translation catalogue has been added.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a3c133e) 89.50% compared to head (301bb72) 89.51%.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1062   +/-   ##
=========================================
  Coverage     89.50%   89.51%           
- Complexity     6315     6316    +1     
=========================================
  Files           824      824           
  Lines         17796    17792    -4     
=========================================
- Hits          15929    15927    -2     
+ Misses         1867     1865    -2     

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