Log the session exception when ownCloud is not installed

lib/base.php

@@ -304,9 +304,12 @@ class OC {
 			self::$session = new \OC\Session\Internal(OC_Util::getInstanceId());
 			// if session cant be started break with http 500 error
 		} catch (Exception $e) {
+			if(!OC_Config::getValue('installed')) {
+				error_log('Session could not be initialized');
+			} else {
 				OC_Log::write('core', 'Session could not be initialized',
 					OC_Log::ERROR);
-
+			}
 			header('HTTP/1.1 500 Internal Server Error');
 			OC_Util::addStyle("styles");
 			$error = 'Session could not be initialized. Please contact your ';