SDL_GameControllerGetAppleSFSymbolsNameForButton() returns NULL if the symbol isn't found

Fixes https://github.com/libsdl-org/SDL/issues/9071

src/joystick/SDL_gamecontroller.c

@@ -3259,10 +3259,11 @@ const char *SDL_GameControllerGetAppleSFSymbolsNameForButton(SDL_GameController
     }
     SDL_UnlockJoysticks();
 
-    return retval;
+    if (retval && *retval) {
-#else
+        return retval;
-    return NULL;
+    }
 #endif
+    return NULL;
 }
 
 const char *SDL_GameControllerGetAppleSFSymbolsNameForAxis(SDL_GameController *gamecontroller, SDL_GameControllerAxis axis)