patch 9.0.0652: 'smoothscroll' not tested with 'number' and "n" in 'cpo'

Problem:    'smoothscroll' not tested with 'number' and "n" in 'cpo'.
Solution:   Add tests, fix uncovered problem.
diff --git a/src/move.c b/src/move.c
index 75cfadf..39b7089 100644
--- a/src/move.c
+++ b/src/move.c
@@ -50,7 +50,7 @@
     {
 	++off;
 	int skip = wp->w_skipcol - width;
-	width -= win_col_off2(wp);
+	width += win_col_off2(wp);
 	while (skip >= width)
 	{
 	    ++off;