C++: Add comment on the existence of reference types

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedExpr.qll

@@ -912,6 +912,7 @@ class TranslatedStructuredBindingVariableAccess extends TranslatedNonConstantExp
   }
 
   private LValueReferenceType getLValueReferenceType() {
+    // The extractor ensures `result` exists when `isNonReferenceStructuredBinding(expr.getTarget())` holds.
     result.getBaseType() = expr.getUnspecifiedType()
   }
 

cpp/ql/lib/semmle/code/cpp/ir/internal/IRUtilities.qll

@@ -41,7 +41,9 @@ Type getVariableType(Variable v) {
         not exists(v.getInitializer()) and result = v.getType()
       else
         if isNonReferenceStructuredBinding(v)
-        then exists(LValueReferenceType r | r.getBaseType() = v.getUnspecifiedType() | result = r)
+        then
+          // The extractor ensures `r` exists when `isNonReferenceStructuredBinding(v)` holds.
+          exists(LValueReferenceType r | r.getBaseType() = v.getUnspecifiedType() | result = r)
         else result = v.getType()
   )
 }