C++: exclude ZeroBounds in relative stage

cpp/ql/lib/experimental/semmle/code/cpp/semantic/analysis/RangeAnalysisImpl.qll

@@ -30,6 +30,10 @@ private module ConstantBounds implements BoundSig<FloatDelta> {
 
 private module RelativeBounds implements BoundSig<FloatDelta> {
   class SemBound instanceof SemanticBound::SemBound {
+    SemBound() {
+      not this instanceof SemanticBound::SemZeroBound
+    }
+
     string toString() { result = super.toString() }
 
     Location getLocation() { result = super.getLocation() }