no error if we try to delete a file which no longer exists

apps/files/ajax/delete.php

@@ -26,7 +26,8 @@ $success = true;
 
 //Now delete
 foreach ($files as $file) {
-	if (!\OC\Files\Filesystem::unlink($dir . '/' . $file)) {
+	if (\OC\Files\Filesystem::file_exists($dir . '/' . $file) &&
+			!\OC\Files\Filesystem::unlink($dir . '/' . $file)) {
 		$filesWithError .= $file . "\n";
 		$success = false;
 	}