Code adjustments after scripted checks

Add an include guard and an additional `#pragme once`. Add comments to
closing namespace scopes.

src/gui/widgets/BarModelEditor.cpp

@@ -67,4 +67,4 @@ void BarModelEditor::paintEvent(QPaintEvent *event)
 	painter.drawText(textRect, m_text);
 }
 
-}
+} // namespace lmms::gui