Bad indentation and missing curly braces in BlockBegin::set_end

SonarClound reports indentation problem near "if (_end != NULL)". It is also not entirely clear if that block misses `_end = NULL`, like the original code had before JDK-8277496.

void BlockBegin::set_end(BlockEnd* new_end) { // Assumes that no predecessor of new_end still has it as its successor
  ...
  // Remove this block as predecessor of its current successors
  if (_end != NULL)
  for (int i = 0; i < number_of_sux(); i++) {
    sux_at(i)->remove_predecessor(this);
  }

Ludvig, please take a look?