Fíx PHP error while accessing non-existant weblink

[ManuelHu]

Pull Request for Issue (none yet)

Summary of Changes

Inspired by https://github.com/joomla/joomla-cms/blob/bef1c83d20024a9970ae4b821dbf2c61c4e4d517/components/com_content/src/Model/ArticleModel.php#L268-L275

Apparently this is needed to properly propagate the 404 error state?

Testing Instructions

• create a menu item for a weblink category (resulting in an URL of /links/)
• append an ID to this URL, i.e. /links/12345. It is important that no weblink or weblink category with this ID exists.
• Also try this with an existing weblink ID

Expected result

• non-existing ID: 404 error is show, no PHP errors
• existing ID: weblink view is shown correctly

Actual result

For the non-existing ID, an error page is shown, but with a PHP error message (instead of a 404):

Fehler: 0 Attempt to assign property "slug" on false


# 	Function 	Location
1 	() 	JROOT/components/com_weblinks/src/View/Weblink/HtmlView.php:62
2 	Joomla\Component\Weblinks\Site\View\Weblink\HtmlView->display() 	JROOT/libraries/src/MVC/Controller/BaseController.php:697
3 	Joomla\CMS\MVC\Controller\BaseController->display() 	JROOT/components/com_weblinks/src/Controller/DisplayController.php:67
4 	Joomla\Component\Weblinks\Site\Controller\DisplayController->display() 	JROOT/libraries/src/MVC/Controller/BaseController.php:730
5 	Joomla\CMS\MVC\Controller\BaseController->execute() 	JROOT/libraries/src/Dispatcher/ComponentDispatcher.php:143
6 	Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch() 	JROOT/libraries/src/Component/ComponentHelper.php:361
7 	Joomla\CMS\Component\ComponentHelper::renderComponent() 	JROOT/libraries/src/Application/SiteApplication.php:218
8 	Joomla\CMS\Application\SiteApplication->dispatch() 	JROOT/libraries/src/Application/SiteApplication.php:261
9 	Joomla\CMS\Application\SiteApplication->doExecute() 	JROOT/libraries/src/Application/CMSApplication.php:306
10 	Joomla\CMS\Application\CMSApplication->execute() 	JROOT/includes/app.php:58
11 	require_once() 	JROOT/index.php:32 

Documentation Changes Required

none