GotoDeskAndPage: the prev argument never works

An incorrect value is assigned to prev_desk_and_page_desk, which makes
`GotoDeskAndPage prev` never working as expected.

fvwm/virtual.c

@@ -2565,6 +2565,7 @@ void CMD_Desk(F_CMD_ARGS)
 void CMD_GotoDeskAndPage(F_CMD_ARGS)
 {
 	int val[3];
+	int current_desk;
 	Bool is_new_desk;
 	char *next;
 	char *token;
@@ -2598,6 +2599,7 @@ void CMD_GotoDeskAndPage(F_CMD_ARGS)
 		return;
 	}
 
+	current_desk = m->virtual_scr.CurrentDesk;
 	is_new_desk = (m->virtual_scr.CurrentDesk != val[0]);
 
 	if (is_tracking_shared && is_new_desk) {
@@ -2606,14 +2608,11 @@ void CMD_GotoDeskAndPage(F_CMD_ARGS)
 		UnmapDesk(m, m->virtual_scr.CurrentDesk, True);
 		CMD_GOTO_DESK(m, val[0]);
 	}
-	m->virtual_scr.prev_desk_and_page_page_x = m->virtual_scr.Vx;
-	m->virtual_scr.prev_desk_and_page_page_y = m->virtual_scr.Vy;
 	MoveViewport(m, val[1], val[2], True);
 	if (is_new_desk)
 	{
-		m->virtual_scr.prev_desk = m->virtual_scr.CurrentDesk;
-		m->virtual_scr.prev_desk_and_page_desk = m->virtual_scr.CurrentDesk;
-		m->virtual_scr.CurrentDesk = val[0];
+		m->virtual_scr.prev_desk = current_desk;
+		m->virtual_scr.prev_desk_and_page_desk = current_desk;
 
 		/* If we're in global mode, store the virtual_scr across all
 		 * monitors.  This will allow for per-monitor tracking to be