patch 9.0.1981: not being able to scroll up in diff mode

Problem:  Cannot scroll up in diff mode with many filler lines and zero
          'scrolloff'.
Solution: Invalidate w_cline_row before calling comp_botline().

closes: #13256

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>
diff --git a/src/move.c b/src/move.c
index ba1eadb..e5309df 100644
--- a/src/move.c
+++ b/src/move.c
@@ -3262,6 +3262,7 @@
 #ifdef FEAT_DIFF
 			curwin->w_topfill = 0;
 #endif
+			curwin->w_valid &= ~(VALID_WROW|VALID_CROW);
 		    }
 		    comp_botline(curwin);
 		    curwin->w_cursor.lnum = curwin->w_botline - 1;
diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index cb042e1..e05d916 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
Binary files differ
diff --git a/src/version.c b/src/version.c
index d7b3c9b..15e87d6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1981,
+/**/
     1980,
 /**/
     1979,