loplugin singlevalfields, need to check default constructor code too

Change-Id: Idcc8de6f1d403a57c59e84774bd7a97e2f3fc224
diff --git a/compilerplugins/clang/singlevalfields.cxx b/compilerplugins/clang/singlevalfields.cxx
index 1a511ab..6d94ef7 100644
--- a/compilerplugins/clang/singlevalfields.cxx
+++ b/compilerplugins/clang/singlevalfields.cxx
@@ -90,6 +90,8 @@ public:
    }

    bool shouldVisitTemplateInstantiations () const { return true; }
    // to catch compiler-generated constructors
    bool shouldVisitImplicitCode() const { return true; }

    bool VisitFieldDecl( const FieldDecl* );
    bool VisitMemberExpr( const MemberExpr* );