backport: Fix a warning if links sticky status isn't set

- initiate its status to false when the link is created
- if not defined, initiate its status to false (can happen if the updater hasn't run)

This is a backport of https://github.com/shaarli/Shaarli/pull/1270

Original author information:

commit b790f900c9
Author: ArthurHoaro <arthur@hoa.ro>
Date:   Sat Feb 9 14:04:16 2019 +0100

Signed-off-by: VirtualTam <virtualtam@flibidi.net>

application/LinkDB.php

@@ -259,7 +259,8 @@ private function check()
             ),
             'private'=>0,
             'created'=> new DateTime(),
-            'tags'=>'opensource software'
+            'tags'=>'opensource software',
+            'sticky' => false,
         );
         $link['shorturl'] = link_small_hash($link['created'], $link['id']);
         $this->links[1] = $link;
@@ -272,6 +273,7 @@ private function check()
             'private'=>1,
             'created'=> new DateTime('1 minute ago'),
             'tags'=>'secretstuff',
+            'sticky' => false,
         );
         $link['shorturl'] = link_small_hash($link['created'], $link['id']);
         $this->links[0] = $link;
@@ -323,6 +325,8 @@ private function read()
                 $link['real_url'] = $link['url'];
             }
 
+            $link['sticky'] = isset($link['sticky']) ? $link['sticky'] : false;
+
             // To be able to load links before running the update, and prepare the update
             if (! isset($link['created'])) {
                 $link['id'] = $link['linkdate'];

index.php

@@ -1179,6 +1179,8 @@ function renderPage($conf, $pluginManager, $LINKSDB, $history, $sessionManager,
             $link['thumbnail'] = $thumbnailer->get($url);
         }
 
+        $link['sticky'] = isset($link['sticky']) ? $link['sticky'] : false;
+
         $pluginManager->executeHooks('save_link', $link);
 
         $LINKSDB[$id] = $link;