don't panic if translation is empty

[nicksnyder]

fixes #95

[codecov]

Codecov Report

Merging #96 into master will increase coverage by 0.73%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #96      +/-   ##
==========================================
+ Coverage   63.13%   63.87%   +0.73%     
==========================================
  Files          27       27              
  Lines        2268     2270       +2     
==========================================
+ Hits         1432     1450      +18     
+ Misses        762      746      -16     
  Partials       74       74

Impacted Files	Coverage Δ
v2/internal/message_template.go	61.53% <100%> (+61.53%)	⬆️
v2/i18n/localizer.go	79.76% <0%> (+2.38%)	⬆️

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