Replace QFontMetrics::width with horizontalAdvance, dark with darker, background() with window() and QString::null with QString()

src/covermanager/albumcoversearcher.cpp

@@ -86,7 +86,7 @@ void SizeOverlayDelegate::paint(QPainter *painter, const QStyleOptionViewItem &o
 
   const QFontMetrics metrics(font);
 
-  const int text_width = metrics.width(text);
+  const int text_width = metrics.horizontalAdvance(text);
 
   const QRect icon_rect(option.rect.left(), option.rect.top(), option.rect.width(), option.rect.width());