Add explicit check for negative overflows in IntegerValue class

[baszoetekouw]

in addition, add tests for IntegerValue::fromInteger to bring coverage for this class to 100%

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.25%. Comparing base (c50b33d) to head (4f863d1).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #100      +/-   ##
============================================
+ Coverage     91.04%   91.25%   +0.21%     
- Complexity      969      971       +2     
============================================
  Files           218      218              
  Lines          3495     3499       +4     
============================================
+ Hits           3182     3193      +11     
+ Misses          313      306       -7     

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[tvdijen]

Thanks Bas!