make it possible to disable installer in config (#11850)

config/global.ini.php

@@ -544,6 +544,9 @@ enable_plugins_admin = 1
 ; an attacker who gained Super User access could execute custom PHP code in a Piwik plugin.
 enable_plugin_upload = 0
 
+; By setting this option to 0 (e.g. in common.config.ini.php) the installer will be disabled.
+enable_installer = 1
+
 ; By setting this option to 0, you can prevent Super User from editing the Geolocation settings.
 enable_geolocation_admin = 1
 

plugins/Installation/Installation.php

@@ -14,6 +14,7 @@ use Piwik\Config;
 use Piwik\FrontController;
 use Piwik\Piwik;
 use Piwik\Plugins\Installation\Exception\DatabaseConnectionFailedException;
+use Piwik\SettingsPiwik;
 use Piwik\View as PiwikView;
 
 /**
@@ -62,6 +63,10 @@ class Installation extends \Piwik\Plugin
     {
         $general = Config::getInstance()->General;
 
+        if (!SettingsPiwik::isPiwikInstalled() && !$general['enable_installer']) {
+            throw new \Exception('Piwik is not set up yet');
+        }
+
         if (empty($general['installation_in_progress'])) {
             return;
         }