JDK-8324890 refactored `_pre_loop_end` field from `CountedLoopNode` to `VLoop`, but missed moving the initialization from relevant constructor:
 https://github.com/openjdk/jdk/commit/232d13688596e9a3c1145ee456dd5a6f7cd1223d#diff-03984204866fcf34c14cb3e5b8ad40348cd60f31af7c937ce6ef7b84e8ea1c69L241

SonarCloud now complains about that field in VLoop:
 1 uninitialized field at the end of the constructor call

The bug looks innocuous so far, but it would potentially skip the assert and return garbage here:

```
  CountedLoopEndNode* pre_loop_end() const {
    assert(cl()->is_main_loop(), "only main loop can reference pre-loop");
    assert(_pre_loop_end != nullptr, "must have found it");
    return _pre_loop_end;
  };
```