work with non existing apps directory. thanks to Antonio for the hint

lib/installer.php

@@ -287,16 +287,17 @@ class OC_Installer{
 	 */
 	public static function installShippedApps(){
 		foreach(OC::$APPSROOTS as $app_dir) {
-			$dir = opendir( $app_dir['path'] );
-			while( false !== ( $filename = readdir( $dir ))){
-				if( substr( $filename, 0, 1 ) != '.' and is_dir($app_dir['path']."/$filename") ){
-					if( file_exists( $app_dir['path']."/$filename/appinfo/app.php" )){
-						if(!OC_Installer::isInstalled($filename)){
-							$info=OC_App::getAppInfo($filename);
-							$enabled = isset($info['default_enable']);
-							if( $enabled ){
-								OC_Installer::installShippedApp($filename);
-								OC_Appconfig::setValue($filename,'enabled','yes');
+			if($dir = opendir( $app_dir['path'] )){
+				while( false !== ( $filename = readdir( $dir ))){
+					if( substr( $filename, 0, 1 ) != '.' and is_dir($app_dir['path']."/$filename") ){
+						if( file_exists( $app_dir['path']."/$filename/appinfo/app.php" )){
+							if(!OC_Installer::isInstalled($filename)){
+								$info=OC_App::getAppInfo($filename);
+								$enabled = isset($info['default_enable']);
+								if( $enabled ){
+									OC_Installer::installShippedApp($filename);
+									OC_Appconfig::setValue($filename,'enabled','yes');
+								}
 							}
 						}
 					}