Consider all levels in theme file check instead of one only

[patrickrobrecht]

Fixes #87. The current maximum of just one level is just removed such that all theme files of any depth are checked.

[codecov-io]

Codecov Report

Merging #90 (de4fe0e) into develop (a8608a3) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             develop      #90   +/-   ##
==========================================
  Coverage      40.29%   40.29%           
  Complexity       147      147           
==========================================
  Files              5        5           
  Lines            546      546           
==========================================
  Hits             220      220           
  Misses           326      326           

Impacted Files	Coverage Δ	Complexity Δ
inc/class-antivirus.php	21.93% <100.00%> (ø)	83.00 <0.00> (ø)

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