BufferView: test and fix scrolling through super long lines

src/core/BufferView.cc

@@ -407,6 +407,7 @@ void BufferView::move_forward_to_screen_position(
                      (it.screen_column() <= m_target_screen_column)))
         {
             *m_iterator = *it.iterator();
+            m_cursor_row_offset = it.row_offset();
         }
         else
         {