message: Convert cout debug message to exception in StructureListBox
diff: #include <NAS2D/Utility.h>
  #include <NAS2D/Renderer/Renderer.h>
  +#include <stdexcept>
  +
  using namespace NAS2D;
  @@ -63,8 +65,7 @@ void StructureListBox::addItem(Structure* structure)
  {
  if (static_cast<StructureListBoxItem*>(item)->structure == structure)
  {
  - std::cout << "StructureListBox::addItem(): annoying bug, fix it." << std::endl;
  - return;
  + throw std::runtime_error("StructureListBox::addItem(): annoying bug, fix it.");
  }
  }
  