Fixed issue #13982 : (partial) some existing Yii cacche can not be used

Dev: test existing method before use it.

application/helpers/update/updatedb_helper.php

@@ -2383,9 +2383,12 @@ function db_upgrade_all($iOldDBVersion, $bSilent = false)
 
     // Try to clear tmp/runtime (database cache files).
     // Related to problems like https://bugs.limesurvey.org/view.php?id=13699.
-    if (!(defined('YII_DEBUG') && YII_DEBUG)) {
+    // Some cache implementations may not have 'flush' method. Only call flush if method exists.
+    if (method_exists(Yii::app()->cache, 'flush')) {
         Yii::app()->cache->flush();
-        // NB: CDummyCache does not have a gc method (used if debug > 0).
+    }
+    // Some cache implementations (ex: CRedisCache, CDummyCache) may not have 'gc' method. Only call gc if method exists.
+    if (method_exists(Yii::app()->cache, 'gc')) {
         Yii::app()->cache->gc();
     }