fix calculation of differential correction

Author: dm61

Loop/Models/RetrospectiveCorrection/IntegralRetrospectiveCorrection.swift

@@ -180,8 +180,10 @@ class IntegralRetrospectiveCorrection: RetrospectiveCorrection {
             // Overall glucose effect calculated as a sum of propotional, integral and differential effects
             proportionalCorrection = IntegralRetrospectiveCorrection.proportionalGain * currentDiscrepancyValue
             // Differential effect added only when negative, to avoid upward stacking with momentum, while still mitigating sluggishness of retrospective correction when discrepancies start decreasing
-            if differentialDiscrepancy < 0 {
+            if differentialDiscrepancy < 0.0 {
                 differentialCorrection = IntegralRetrospectiveCorrection.differentialGain * differentialDiscrepancy
+            } else {
+                differentialCorrection = 0.0
             }
             let totalCorrection = proportionalCorrection + integralCorrection + differentialCorrection
             totalGlucoseCorrectionEffect = HKQuantity(unit: unit, doubleValue: totalCorrection)