patch 8.0.1220: skipping empty statusline groups is not correct

Problem:    Skipping empty statusline groups is not correct.
Solution:   Also set group_end_userhl. (itchyny)
diff --git a/src/buffer.c b/src/buffer.c
index 0d69b9d..dad9103 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -4028,9 +4028,14 @@
 		/* remove group if all items are empty and highlight group
 		 * doesn't change */
 		group_start_userhl = group_end_userhl = 0;
-		for (n = 0; n < groupitem[groupdepth]; n++)
+		for (n = groupitem[groupdepth] - 1; n >= 0; n--)
+		{
 		    if (item[n].type == Highlight)
-			group_start_userhl = item[n].minwid;
+		    {
+			group_start_userhl = group_end_userhl = item[n].minwid;
+			break;
+		    }
+		}
 		for (n = groupitem[groupdepth] + 1; n < curitem; n++)
 		{
 		    if (item[n].type == Normal)