Implement the size of an assembly stream

This will make it possible to act propely on moves of future files if we
need to know the size (like for max size virus scanning).

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

apps/dav/lib/Upload/AssemblyStream.php

@@ -170,7 +170,9 @@ class AssemblyStream implements \Icewind\Streams\File {
 	 * @return array
 	 */
 	public function stream_stat() {
-		return [];
+		return [
+			'size' => $this->size,
+		];
 	}
 
 	/**