patch 8.1.1570: icon signs not displayed properly in the number column

Problem:    Icon signs not displayed properly in the number column.
Solution:   Display them properly. (Yegappan Lakshmanan, closes #4559)
diff --git a/src/gui.c b/src/gui.c
index a4673f0..5689182 100644
--- a/src/gui.c
+++ b/src/gui.c
@@ -2253,6 +2253,7 @@
     int		col = gui.col;
 #ifdef FEAT_SIGN_ICONS
     int		draw_sign = FALSE;
+    char_u	extra[18];
 # ifdef FEAT_NETBEANS_INTG
     int		multi_sign = FALSE;
 # endif
@@ -2275,10 +2276,17 @@
 	    multi_sign = TRUE;
 # endif
 	/* draw spaces instead */
-	s = (char_u *)"  ";
+	if (*curwin->w_p_scl == 'n' && *(curwin->w_p_scl + 1) == 'u' &&
+		(curwin->w_p_nu || curwin->w_p_rnu))
+	{
+	    sprintf((char *)extra, "%*c ", number_width(curwin), ' ');
+	    s = extra;
+	}
+	else
+	    s = (char_u *)"  ";
 	if (len == 1 && col > 0)
 	    --col;
-	len = 2;
+	len = (int)STRLEN(s);
 	draw_sign = TRUE;
 	highlight_mask = 0;
     }