Contact form loses data after postback with error (#17743)

* Contact form loses data after postback with error

Pull Request for issue #17126.

Testing Instructions. See issue #17126
* Go to Single Contact. 
* Fill in the form. 
* Do not fill in captcha.
* Send email.

Expected result:  
Warning + textboxes are NOT empty. 
So the user should not entered all text again.

Actual result:
All textboxes are empty, so the user has to enter again all textboxes.

Thanks to: 
@ pascal-910.

* Delete some tabs

Delete some tabs.

* Update view.html.php

if (!isset($item->catid) || empty($item->catid)) changes to if (empty($item->catid))

components/com_contact/views/contact/view.html.php

@@ -72,7 +72,10 @@ public function display($tpl = null)
 		$item = $this->get('Item');
 		$state = $this->get('State');
 
-		$app->setUserState('com_contact.contact.data', array('catid' => $item->catid));
+		if (empty($item->catid))
+		{
+			$app->setUserState('com_contact.contact.data', array('catid' => $item->catid));
+		}
 
 		$this->form = $this->get('Form');