patch 9.1.0258: half-page scrolling broke backward compatibility

Problem:  Support for 'smoothscroll' in (half-)page scrolling
          broke backward compatibility and can be made to work better.
          (after v9.1.215)
Solution: Restore the previous cursor and end-of-buffer behavior for
          half-page scrolling and improve 'smoothscroll' support.
          (Luuk van Baal)

fixes: #14338
closes: #14377

Signed-off-by: Luuk van Baal <luukvbaal@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index 344571f..b8d0057 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
Binary files differ