Fix SQL error on logout when using session_storage=php (#1490421)

CHANGELOG

@@ -2,6 +2,7 @@ CHANGELOG Roundcube Webmail
 ===========================
 
 - Fix "Importing..." message does not hide on error (#1490422)
+- Fix SQL error on logout when using session_storage=php (#1490421)
 
 RELEASE 1.1.2
 -------------

program/lib/Roundcube/rcube_session.php

@@ -144,7 +144,15 @@ class rcube_session
      */
     public function destroy($key)
     {
-        return $this->memcache ? $this->mc_destroy($key) : $this->db_destroy($key);
+        if ($this->storage == 'memcache' && $this->memcache) {
+            return $this->mc_destroy($key);
+        }
+        else if ($this->storage == 'db') {
+            return $this->db_destroy($key);
+        }
+        else {
+            return true;
+        }
     }