path: Use close_path() for closing paths (#801)

library/src/visualize/path.rs

@@ -123,6 +123,7 @@ impl Layout for PathElem {
             let to_point = points[0];
 
             add_cubic(from_point, to_point, from, to);
+            path.close_path();
         }
 
         // Prepare fill and stroke.

tests/typ/visualize/path.typ

@@ -30,6 +30,13 @@
     ((30%, 60%), (-20%, 0%), (0%, 0%)),
     ((50%, 30%), (60%, -30%), (60%, 0%)),
   ),
+  path(
+    stroke: 5pt,
+    closed: true,
+    (0pt,  30pt),
+    (30pt, 30pt),
+    (15pt, 0pt),
+  ),
 )
 
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