patch 8.1.1613: popup window test fails with Athena and Motif

Problem:    Popup window test fails with Athena and Motif.
Solution:   Compute the highlight attribut when the GUI is not active.
diff --git a/src/syntax.c b/src/syntax.c
index 4d42346..9c17a58 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -8202,6 +8202,8 @@
 	{
 	    if (gui.in_use && do_colors)
 		gui_new_scrollbar_colors();
+	    else
+		set_hl_attr(idx);
 	}
 # ifdef FEAT_BEVAL_GUI
 	else if (is_tooltip_group)