udf: Handle error when adding extent to a file

commit 19fd80de upstream.

When adding extent to a file fails, so far we've silently squelshed the
error. Make sure to propagate it up properly.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>