This is to prevent NULL pointers when creating a standalone text service that doesn't have any text set and then using functions like EM_SETSEL. This NULL pointers doesn't happen when creating a richedit windows, because it sets an empty text when the richedit window procedure handles the WM_CREATE event.
-- v3: riched20: Check if row is null in editor_ensure_visible. riched20: Return NULL if no row is found in row_from_cursor.