Make sure that we have a stream

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

apps/dav/lib/Connector/Sabre/File.php

@@ -167,6 +167,13 @@ class File extends Node implements IFile {
 			}
 
 			if ($partStorage->instanceOfStorage(Storage\IWriteStreamStorage::class)) {
+
+				if (!is_resource($data)) {
+					$data = fopen('php://temp', 'r+');
+					fwrite($data, 'foobar');
+					rewind($data);
+				}
+
 				$isEOF = false;
 				$wrappedData = CallbackWrapper::wrap($data, null, null, null, null, function($stream) use (&$isEOF) {
 					$isEOF = feof($stream);