Merge pull request #13842 from owncloud/is_file_2_is_readable

check if cache files are readable

lib/private/cache/file.php

@@ -83,7 +83,7 @@ class File {
 
 	public function hasKey($key) {
 		$storage = $this->getStorage();
-		if ($storage && $storage->is_file($key)) {
+		if ($storage && $storage->is_file($key) && $storage->isReadable($key)) {
 			return true;
 		}
 		return false;

lib/private/cache/fileglobal.php

@@ -52,7 +52,7 @@ class FileGlobal {
 	public function hasKey($key) {
 		$key = $this->fixKey($key);
 		$cache_dir = self::getCacheDir();
-		if ($cache_dir && is_file($cache_dir.$key)) {
+		if ($cache_dir && is_file($cache_dir.$key) && is_readable($cache_dir.$key)) {
 			$mtime = filemtime($cache_dir.$key);
 			if ($mtime < time()) {
 				unlink($cache_dir.$key);