Add check for zero denominator in SafeLong constructor
Add check for zero denominator in SafeLong constructor

adampingel/spire,codeaudit/spire,JackSullivan/spire,kevinmeredith/spire,non/spire,rklaehn/spire,tixxit/spire,guersam/spire,codeaudit/spire,non/spire,adampingel/spire,tixxit/spire,siddhartha-gadgil/spire,kevinmeredith/spire,JackSullivan/spire,rklaehn/spire,guersam/spire,siddhartha-gadgil/spire