Uninitialized klassVtable::_verify_count field

SonarCloud reports an uninitialized field in `klassVtable::_verify_count`.

```
class klassVtable {
#ifndef PRODUCT
  int _verify_count; // to make verify faster
#endif
```

There is at least one use that touches the uninitialized value:

```
#ifndef PRODUCT
  // avoid redundant verifies
  if (!forced && _verify_count == Universe::verify_count()) return;
  _verify_count = Universe::verify_count();
#endif
```