fixed exception in case no blubber streams could be found, closes #864

Closes #864

Merge request studip/studip!1073

app/controllers/blubber.php

@@ -45,16 +45,16 @@ class BlubberController extends AuthenticatedController
             $this->thread = array_pop($threads);
         }
 
+        $this->thread_data = [];
         if ($this->thread) {
             $this->thread->markAsRead();
+            $this->thread_data = $this->thread->getJSONData(
+                50,
+                null,
+                Request::get("search")
+            );
         }
 
-        $this->thread_data = $this->thread->getJSONData(
-            50,
-            null,
-            Request::get("search")
-        );
-
         if (!Avatar::getAvatar($GLOBALS['user']->id)->is_customized() && !$_SESSION['already_asked_for_avatar']) {
             $_SESSION['already_asked_for_avatar'] = true;
             PageLayout::postInfo(sprintf(

app/views/blubber/index.php

 <div class="blubber_panel"
-     data-active_thread="<?= htmlReady($thread->getId()) ?>"
+     data-active_thread="<?= htmlReady(!empty($thread) ? $thread->getId() : '') ?>"
      data-thread_data="<?= htmlReady(json_encode($thread_data ?: ['thread_posting' => []])) ?>"
      data-threads_more_down="<?= htmlReady($threads_more_down) ?>"
      :class="waiting ? 'waiting' : ''">