.ai save: graph round trips leave out the art bounds the reader measures

Opening an .ai graph now sets placed_art from the art as read (main's d3789f2b0c), so the comparison in the graph round-trip tests leaves it out, as it already leaves out placed.

crates/eps/src/ai_graph.rs

@@ -592,6 +592,7 @@ pub(crate) mod sample {
             blanks: vec![],
             series_paints: vec![],
             placed: None,
+            placed_art: None,
             series_kinds: vec![],
             ..g.clone()
         };