non-specific search dictionary

[trishorts]

user dmorgan reported issue during non-specific search of key already existing.

#2400

This PR adds cod the check the dictionary for existence of a key before adding.

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 8 lines in your changes missing coverage. Please review.

Project coverage is 93.70%. Comparing base (1d402e2) to head (73eb70b).

Files	Patch %	Lines
...cificEnzymeSearch/NonSpecificEnzymeSearchEngine.cs	42.85%	6 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2401      +/-   ##
==========================================
+ Coverage   93.65%   93.70%   +0.04%     
==========================================
  Files         140      140              
  Lines       21896    21908      +12     
  Branches     3005     3007       +2     
==========================================
+ Hits        20506    20528      +22     
+ Misses        934      925       -9     
+ Partials      456      455       -1     

Files	Coverage Δ
...cificEnzymeSearch/NonSpecificEnzymeSearchEngine.cs	89.54% <42.85%> (+2.07%)	⬆️