Fix off-by-one.

CCBUG:373075

libtaskmanager/abstractwindowtasksmodel.cpp

@@ -41,7 +41,7 @@ AbstractWindowTasksModel::AbstractWindowTasksModel(QObject *parent)
     auto screenAdded = [this](const QScreen *screen) {
         connect(screen, &QScreen::geometryChanged, this,
             [this]() {
-                dataChanged(index(0, 0), index(rowCount(), 0), QVector<int>{ScreenGeometry});
+                dataChanged(index(0, 0), index(rowCount() - 1, 0), QVector<int>{ScreenGeometry});
             }
         );
     };