Fix #3544: an artboard name XML can't hold falls back to the document title

Review follow-up (CodeRabbit): the blank-name check ran on the raw name, so
a name made only of characters XML can't hold (control characters) wrote an
empty <title>. The name is sanitised first, then the fallback applies. The
title test covers such a name; it fails without the change.

crates/svg/src/export.rs

@@ -134,11 +134,12 @@ fn write(doc: &Document, opts: &ExportOptions, native: Option<&[u8]>, id_prefix:
         out.push_str(&format!("</defs>{nl}"));
     }
     // An artboard exported on its own is named after it (#3544), else after the document.
-    let board = opts.artboard.filter(|_| opts.artboard_title).and_then(|i| doc.artboards.get(i)).map(|a| a.name.as_str());
-    let title = board.filter(|n| !n.trim().is_empty()).unwrap_or(&doc.title);
+    // A name that is blank once the characters XML can't hold are dropped falls back too.
+    let board = opts.artboard.filter(|_| opts.artboard_title).and_then(|i| doc.artboards.get(i)).map(|a| xml_text(&a.name));
+    let title = board.filter(|n| !n.trim().is_empty()).unwrap_or_else(|| xml_text(&doc.title));
     if !title.is_empty() {
         out.push_str(&w.indent(1));
-        out.push_str(&format!("<title>{}</title>{nl}", xml_text(title)));
+        out.push_str(&format!("<title>{title}</title>{nl}"));
     }
     // File Info's description.
     if !doc.metadata.description.trim().is_empty() {

crates/svg/tests/title_control_chars.rs

@@ -51,4 +51,7 @@ fn an_artboard_exported_alone_is_titled_after_it() {
     // An unnamed artboard falls back to the document's title.
     d.artboards[1].name = " ".into();
     assert_eq!(title(&d, alone(Some(1))).as_deref(), Some("<title>Icons</title>"));
+    // So does one whose only characters can't appear in XML.
+    d.artboards[1].name = "\u{1}\u{2}".into();
+    assert_eq!(title(&d, alone(Some(1))).as_deref(), Some("<title>Icons</title>"));
 }