[TheTVDb] Fix firstAired scraper; Allow IMDB id's with 8 digits

[bugwelle]

No description provided.

[codecov-io]

Codecov Report

Merging #855 into master will decrease coverage by <.01%.
The diff coverage is 12.5%.

@@            Coverage Diff            @@
##           master    #855      +/-   ##
=========================================
- Coverage    6.98%   6.98%   -0.01%     
=========================================
  Files         445     445              
  Lines       34175   34176       +1     
=========================================
  Hits         2387    2387              
- Misses      31788   31789       +1

Impacted Files	Coverage Δ
src/scrapers/tv_show/TheTvDb/Search.cpp	0% <0%> (ø)	⬆️
src/scrapers/tv_show/TheTvDb/ShowParser.cpp	0% <0%> (ø)	⬆️
src/ui/movies/MovieMultiScrapeDialog.cpp	0% <0%> (ø)	⬆️
src/scrapers/tv_show/TheTvDb/EpisodeParser.cpp	0% <0%> (ø)	⬆️
src/data/ImdbId.cpp	57.89% <100%> (ø)	⬆️

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