Verify return type

Can also be null. Silences another security warning...

lib/private/files/view.php

@@ -1253,7 +1253,7 @@ class View {
 	 * @param boolean|string $includeMountPoints true to add mountpoint sizes,
 	 * 'ext' to add only ext storage mount point sizes. Defaults to true.
 	 * defaults to true
-	 * @return \OC\Files\FileInfo|bool False if file does not exist
+	 * @return \OC\Files\FileInfo|false False if file does not exist
 	 */
 	public function getFileInfo($path, $includeMountPoints = true) {
 		$this->assertPathLength($path);

lib/private/preview.php

@@ -1250,7 +1250,7 @@ class Preview {
 	 * @param array $args
 	 * @param string $prefix
 	 */
-	public static function prepare_delete($args, $prefix = '') {
+	public static function prepare_delete(array $args, $prefix = '') {
 		$path = $args['path'];
 		if (substr($path, 0, 1) === '/') {
 			$path = substr($path, 1);
@@ -1259,7 +1259,11 @@ class Preview {
 		$view = new \OC\Files\View('/' . \OC_User::getUser() . '/' . $prefix);
 
 		$absPath = Files\Filesystem::normalizePath($view->getAbsolutePath($path));
-		self::addPathToDeleteFileMapper($absPath, $view->getFileInfo($path));
+		$fileInfo = $view->getFileInfo($path);
+		if($fileInfo === false) {
+			return;
+		}
+		self::addPathToDeleteFileMapper($absPath, $fileInfo);
 		if ($view->is_dir($path)) {
 			$children = self::getAllChildren($view, $path);
 			self::$deleteChildrenMapper[$absPath] = $children;