Refresh the grid correctly when the selection mode changes

Update the cells that had to be deselected due to the selection mode
change.

This used to work, but the refresh was lost during a previous
refactoring.

src/generic/gridsel.cpp

@@ -128,7 +128,13 @@ void wxGridSelection::SetSelectionMode( wxGrid::wxGridSelectionModes selmode )
             }
 
             if ( !valid )
+            {
+                if ( !m_grid->GetBatchCount() )
+                {
+                    m_grid->RefreshBlock(block.GetTopLeft(), block.GetBottomRight());
+                }
                 m_selection.erase(m_selection.begin() + n);
+            }
         }
 
         m_selectionMode = selmode;