message: Use ListBox::selected() for ComboBox::selectionText()
diff: #include "ComboBox.h"
  +#include "../../Constants/Strings.h"
  +
  #include <NAS2D/Utility.h>
  #include <NAS2D/MathUtils.h>
  @@ -118,7 +120,7 @@ void ComboBox::clearSelection()
  */
  void ComboBox::lstItemsSelectionChanged()
  {
  - txtField.text(lstItems.selectionText());
  + txtField.text(selectionText());
  lstItems.visible(false);
  mRect = mBaseArea;
  mSelectionChanged();
  @@ -158,7 +160,7 @@ void ComboBox::addItem(const std::string& item, int tag)
  */
  const std::string& ComboBox::selectionText() const
  {
  - return lstItems.selectionText();
  + return lstItems.isItemSelected() ? lstItems.selected().text : constants::EMPTY_STR;
  }
  @@ -173,7 +175,7 @@ int ComboBox::selectionTag() const
  void ComboBox::currentSelection(std::size_t index) {
  lstItems.currentSelection(index);
  - text(lstItems.selectionText());
  + text(selectionText());
  mSelectionChanged();
  }
  