patch 9.0.1000: with 'smoothscroll' skipcol may be reset unnecessarily

Problem:    With 'smoothscroll' skipcol may be reset unnecessarily.
Solution:   Check the line does actually fit in the window.
diff --git a/src/move.c b/src/move.c
index d976697..7a9ae3e 100644
--- a/src/move.c
+++ b/src/move.c
@@ -1909,7 +1909,11 @@
     int	    scrolled = FALSE;
 
     validate_cheight();
-    if (curwin->w_cline_height == curwin->w_height)
+    if (curwin->w_cline_height == curwin->w_height
+	    // w_cline_height may be capped at w_height, check there aren't
+	    // actually more lines.
+	    && plines_win(curwin, curwin->w_cursor.lnum, FALSE)
+							   <= curwin->w_height)
     {
 	// the line just fits in the window, don't scroll
 	reset_skipcol();