Fix fatal error in database_attachments plugin under some conditions (#1489726)

Conflicts:

	CHANGELOG

CHANGELOG

@@ -14,6 +14,7 @@ RELEASE 1.0.0
 - Fix invalid X-Draft-Info on forwarded message draft (#1489587)
 - Fix regression in handling of 'attachments' result in message_compose hook (#1489627)
 - Fix issue where msgexport.sh printed the message to STDOUT instead of a file (#1489634)
+- Fix fatal error in database_attachments plugin under some conditions (#1489726)
 
 RELEASE 1.0-rc
 --------------

plugins/database_attachments/database_attachments.php

@@ -126,8 +126,10 @@ class database_attachments extends filesystem_attachments
      */
     function cleanup($args)
     {
-        $cache = $this->get_cache();
-        $cache->remove($args['group'], true);
+        // check if cache object exist, it may be empty on session_destroy (#1489726)
+        if ($cache = $this->get_cache()) {
+            $cache->remove($args['group'], true);
+        }
     }
 
     /**