Edge Case Issue - Caused by unsafe initilization of lowerIndex/upperIndex vars in QuickDecomp

[2chivi]

Initializing lowerIndex at 0 is unsafe and causes some Edge Case miscalculations and bizarre artifacts. The 2nd code snippet shows where lowerIndex(0) could equal (upperIndex+1)%poly.length if upperIndex is poly.length-1. Even when lowerIndex was never actually calculated.

This code is from polygonQuickDecomp

                var upperInt = [0, 0], lowerInt = [0, 0], p = [0, 0]; // Points
                var upperDist = 0, lowerDist = 0, d = 0, closestDist = 0; // scalars
                var upperIndex = 0, lowerIndex = 0, closestIndex = 0;

if (lowerIndex === (upperIndex + 1) % polygon.length) {

[PraxTube]

Do you have an example where this is a problem? Also how would you handle this case?