patch 9.0.0671: negative topline using CTRL-Y with 'smoothscroll' and 'diff'

Problem:    Negative topline using CTRL-Y with 'smoothscroll' and 'diff'.
            (Ernie Rael)
Solution:   Only use 'smoothscroll' when 'wrap' is set.

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    671,
 /**/
     670,
 /**/