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;