Avoid a segfault when services_discovery_GetServicesNames fail.

modules/gui/qt4/menus.cpp

@@ -428,6 +428,9 @@ QMenu *QVLCMenu::SDMenu( intf_thread_t *p_intf )
     char **ppsz_longnames;
     char **ppsz_names = services_discovery_GetServicesNames( p_intf,
                                                              &ppsz_longnames );
+    if( !ppsz_names )
+        return menu;
+
     char **ppsz_name = ppsz_names, **ppsz_longname = ppsz_longnames;
     for( ; *ppsz_name; ppsz_name++, ppsz_longname++ )
     {

modules/gui/wxwidgets/dialogs/playlist.cpp

@@ -1408,6 +1408,9 @@ wxMenu *Playlist::SDMenu()
     char **ppsz_longnames;
     char **ppsz_names = services_discovery_GetServicesNames( p_playlist,
                                                              &ppsz_longnames );
+    if( !ppsz_names )
+        return p_sd_menu;
+
     char **ppsz_name = ppsz_names, **ppsz_longname = ppsz_longnames;
 
     int i_number = 0;

modules/misc/lua/sd.c

@@ -50,6 +50,9 @@ int vlclua_sd_get_services_names( lua_State *L )
     vlc_object_t *p_this = vlclua_get_this( L );
     char **ppsz_longnames;
     char **ppsz_names = services_discovery_GetServicesNames( p_this, &ppsz_longnames );
+    if( !ppsz_names )
+        return 0;
+
     char **ppsz_longname = ppsz_longnames;
     char **ppsz_name = ppsz_names;
     lua_settop( L, 0 );