wmaker: prevent transient windows to create an appicon

This patch is preventing transient windows which are defined as
short-lived window that "belongs" to a main application window
to create their own appicon.
Some applications are not creating an appicon but are getting
default appicon for their popup windows which can only disappear
when wmaker is restarted.

src/appicon.c

@@ -146,6 +146,10 @@ WAppIcon *wAppIconCreateForDock(WScreen *scr, const char *command, const char *w
 
 void create_appicon_for_application(WApplication *wapp, WWindow *wwin)
 {
+	/* Transient windows should never get their own appicon */
+	if (wwin->transient_for != None && wwin->transient_for != wwin->screen_ptr->root_win)
+		return;
+
 	/* Try to create an icon from the dock or clip */
 	create_appicon_from_dock(wwin, wapp, wapp->main_window);