patch 9.0.1564: display moves up and down with 'incsearch' and 'smoothscroll'

Problem:    Display moves up and down with 'incsearch' and 'smoothscroll'.
Solution:   Do not check if w_skipcol changed. (Luuk van Baal, closes #12410,
            closes #12409)
diff --git a/src/move.c b/src/move.c
index 93c101b..3f6802a 100644
--- a/src/move.c
+++ b/src/move.c
@@ -312,7 +312,6 @@
 	*so_ptr = mouse_dragging - 1;
 
     linenr_T old_topline = curwin->w_topline;
-    colnr_T old_skipcol = curwin->w_skipcol;
 #ifdef FEAT_DIFF
     int old_topfill = curwin->w_topfill;
 #endif
@@ -517,8 +516,8 @@
 	dollar_vcol = -1;
 	redraw_later(UPD_VALID);
 
-	// Only reset w_skipcol if it was not just set to make cursor visible.
-	if (curwin->w_skipcol == old_skipcol)
+	// When 'smoothscroll' is not set, should reset w_skipcol.
+	if (!curwin->w_p_sms)
 	    reset_skipcol();
 
 	// May need to set w_skipcol when cursor in w_topline.