Fix icon-only delegate

The delegate was still rendering display text. But we didn't realize
because the only place where this delegate was used was returning a
QVariant() for DisplayText role earlier. Once we started returning a
valid QString (for copy-paste purposes), this bug showed up.

This didn't work because we further delegate the actual painting to
the base QStyledItemDelegate which re-initializes option.features
from the item index values, so removing HasDisplay does not work.

The fix is to override the displayText() to return a null string.

client/icononlydelegate.h

@@ -31,9 +31,13 @@ class IconOnlyDelegate : public QStyledItemDelegate
     {
         QStyleOptionViewItem opt = option;
         opt.decorationPosition = QStyleOptionViewItem::Top;
-        opt.features &= ~QStyleOptionViewItem::HasDisplay;
         QStyledItemDelegate::paint(painter, opt, index);
     }
+
+    QString displayText(const QVariant&, const QLocale&) const
+    {
+        return QString();
+    }
 };
 
 #endif