CtfVisualizer: Avoid compile warning

Column::COUNT should not show up as actual column, but the compiler
doesn't know.

Change-Id: I68eea5c73a95bd45378f88c505f0cefed62ce8ab
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/ctfvisualizer/ctfstatisticsmodel.cpp

@@ -93,6 +93,9 @@ QVariant CtfStatisticsModel::data(const QModelIndex &index, int role) const
         case Column::AvgDuration:
         case Column::MaxDuration:
             return Qt::AlignRight;
+        default:
+            Q_UNREACHABLE();
+            return QVariant();
         }
     case SortRole:
         switch (index.column()) {