patch 9.0.0645: CTRL-Y does not stop at line 1

Problem:    CTRL-Y does not stop at line 1. (John Marriott)
Solution:   Stop at line 1 when 'smoothscroll' is not set. (closes #11261)
diff --git a/src/move.c b/src/move.c
index dca77f7..43e3273 100644
--- a/src/move.c
+++ b/src/move.c
@@ -1485,11 +1485,14 @@
 	else
 #endif
 	{
-	    if (curwin->w_topline == 1 && curwin->w_skipcol < width1)
+	    // break when at the very top
+	    if (curwin->w_topline == 1
+			   && (!curwin->w_p_sms || curwin->w_skipcol < width1))
 		break;
 	    if (curwin->w_p_wrap && curwin->w_p_sms
-						  && curwin->w_skipcol >= width1)
+						&& curwin->w_skipcol >= width1)
 	    {
+		// scroll a screen line down
 		if (curwin->w_skipcol >= width1 + width2)
 		    curwin->w_skipcol -= width2;
 		else
@@ -1499,6 +1502,7 @@
 	    }
 	    else
 	    {
+		// scroll a text line down
 		--curwin->w_topline;
 		curwin->w_skipcol = 0;
 #ifdef FEAT_DIFF