tableview: Fix index error when displaying dataset with zero columns (#6779)

Author: ales-erjavec

Orange/widgets/data/utils/tableview.py

@@ -168,7 +168,8 @@ def __headerDataChanged(
             model = self.model()
             model = source_model(model)
             if isinstance(model, RichTableModel) and \
-                    model.richHeaderFlags() & RichTableModel.Labels:
+                    model.richHeaderFlags() & RichTableModel.Labels and \
+                    model.columnCount() > 0:
                 items = model.headerData(
                     0, Qt.Horizontal, RichTableModel.LabelsItemsRole
                 )

Orange/widgets/data/utils/tests/test_tableview.py

@@ -31,6 +31,19 @@ def test_tableview(self):
         model.setRichHeaderFlags(RichTableModel.Name)
         self.assertEqual(view.cornerText(), "")
 
+    def test_tableview_empty_model(self):
+        data = Orange.data.Table.from_list(
+            Orange.data.Domain([], None),
+            [],
+        )
+        view = RichTableView()
+        model = RichTableModel(data)
+        view.setModel(model)
+        self.assertIsInstance(view.selectionModel(), BlockSelectionModel)
+        model.setRichHeaderFlags(RichTableModel.Name | RichTableModel.Labels |
+                                 RichTableModel.Icon)
+        view.grab()
+
     def test_tableview_toggle_select_all(self):
         view = RichTableView()
         model = RichTableModel(self.data)