Avoid errors when trying to lock config if database is not yet available (#4603)

Author: colinmollenhour

app/code/core/Mage/Core/Model/Config.php

@@ -526,6 +526,9 @@ public function getCacheSaveLock($waitTime = null, $ignoreFailure = false)
         }
         $waitTime = $waitTime ?: (getenv('MAGE_CONFIG_CACHE_LOCK_WAIT') ?: (PHP_SAPI === 'cli' ? 60 : 3));
         $connection = Mage::getSingleton('core/resource')->getConnection('core_write');
+        if (!$connection) {
+            return;
+        }
         if (!$connection->fetchOne("SELECT GET_LOCK('core_config_cache_save_lock', ?)", [$waitTime])) {
             if ($ignoreFailure) {
                 return;
@@ -550,6 +553,9 @@ public function releaseCacheSaveLock()
             return;
         }
         $connection = Mage::getSingleton('core/resource')->getConnection('core_write');
+        if (!$connection) {
+            return;
+        }
         $connection->fetchOne("SELECT RELEASE_LOCK('core_config_cache_save_lock')");
     }