8331863: DUIterator_Fast used before it is constructed

Reviewed-by: stuefe
Backport-of: 20927ac8405b4adca463e4c691ea573abdac1c4f

Author: RadekCap

src/hotspot/share/opto/node.hpp

@@ -1455,8 +1455,8 @@ Node* Node::last_out(DUIterator_Last& i) const {
 class SimpleDUIterator : public StackObj {
  private:
   Node* node;
-  DUIterator_Fast i;
   DUIterator_Fast imax;
+  DUIterator_Fast i;
  public:
   SimpleDUIterator(Node* n): node(n), i(n->fast_outs(imax)) {}
   bool has_next() { return i < imax; }