Fix instrumentation error for virtual modifiers

[cgewecke]

#766

Updates parsing to check that modifier definitions have a body before instrumenting them (like functions)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (70de9d4) 96.48% compared to head (997ce70) 96.48%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #832   +/-   ##
=======================================
  Coverage   96.48%   96.48%           
=======================================
  Files          19       19           
  Lines        1053     1054    +1     
=======================================
+ Hits         1016     1017    +1     
  Misses         37       37           

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