Show only unread when selecting unread

Before, when there was no unread articles, all articles where displayed. This behaviour was not the one intended.
Now, when there is no unread articles, a message is displayed to alert that there is no article.

See #428

Correction after comment

app/Controllers/indexController.php

@@ -84,6 +84,7 @@ class FreshRSS_index_Controller extends Minz_ActionController {
 
 		// On récupère les différents éléments de filtrage
 		$this->view->state = $state = Minz_Request::param ('state', $this->view->conf->default_view);
+		$state_param = Minz_Request::param ('state', null);
 		$filter = Minz_Request::param ('search', '');
 		if (!empty($filter)) {
 			$state = 'all';	//Search always in read and unread articles
@@ -111,7 +112,7 @@ class FreshRSS_index_Controller extends Minz_ActionController {
 					$hasUnread = true;
 					break;
 			}
-			if (!$hasUnread) {
+			if (!$hasUnread && is_null($state_param)) {
 				$this->view->state = $state = 'all';
 			}
 		}
@@ -129,7 +130,7 @@ class FreshRSS_index_Controller extends Minz_ActionController {
 
 			// Si on a récupéré aucun article "non lus"
 			// on essaye de récupérer tous les articles
-			if ($state === 'not_read' && empty($entries)) {
+			if ($state === 'not_read' && empty($entries) && is_null($state_param)) {
 				Minz_Log::record ('Conflicting information about nbNotRead!', Minz_Log::DEBUG);
 				$this->view->state = 'all';
 				$entries = $entryDAO->listWhere($getType, $getId, 'all', $order, $nb, $first, $filter, $date_min, $keepHistoryDefault);