wayland: Use libdecor visibility toggle for hiding/showing the window

The current method of toggling the libdecor window visibility by destroying and recreating the frame results in a race where a use-after-free bug can manifest itself within libdecor when window visibility is toggled quickly. Instead, use the libdecor function for toggling visibility instead of destroying and recreating the frame every time.

src/video/wayland/SDL_waylandwindow.c

@@ -1228,15 +1228,20 @@ void Wayland_ShowWindow(_THIS, SDL_Window *window)
     /* Create the shell surface and map the toplevel/popup */
 #ifdef HAVE_LIBDECOR_H
     if (WINDOW_IS_LIBDECOR(c, window)) {
-        data->shell_surface.libdecor.frame = libdecor_decorate(c->shell.libdecor,
-                                                               data->surface,
-                                                               &libdecor_frame_interface,
-                                                               data);
-        if (data->shell_surface.libdecor.frame == NULL) {
-            SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "Failed to create libdecor frame!");
+        if (data->shell_surface.libdecor.frame) {
+            /* If the frame already exists, just set the visibility. */
+            libdecor_frame_set_visibility(data->shell_surface.libdecor.frame, true);
         } else {
-            libdecor_frame_set_app_id(data->shell_surface.libdecor.frame, c->classname);
-            libdecor_frame_map(data->shell_surface.libdecor.frame);
+            data->shell_surface.libdecor.frame = libdecor_decorate(c->shell.libdecor,
+                                                                   data->surface,
+                                                                   &libdecor_frame_interface,
+                                                                   data);
+            if (data->shell_surface.libdecor.frame == NULL) {
+                SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "Failed to create libdecor frame!");
+            } else {
+                libdecor_frame_set_app_id(data->shell_surface.libdecor.frame, c->classname);
+                libdecor_frame_map(data->shell_surface.libdecor.frame);
+            }
         }
     } else
 #endif
@@ -1425,8 +1430,7 @@ void Wayland_HideWindow(_THIS, SDL_Window *window)
 #ifdef HAVE_LIBDECOR_H
     if (WINDOW_IS_LIBDECOR(data, window)) {
         if (wind->shell_surface.libdecor.frame) {
-            libdecor_frame_unref(wind->shell_surface.libdecor.frame);
-            wind->shell_surface.libdecor.frame = NULL;
+            libdecor_frame_set_visibility(wind->shell_surface.libdecor.frame, false);
         }
     } else
 #endif