Don't generate impl-items div container if there is none

src/librustdoc/html/render/mod.rs

@@ -1667,10 +1667,12 @@ fn render_impl(
             );
         }
     }
+    if !default_impl_items.is_empty() || !impl_items.is_empty() {
         w.write_str("<div class=\"impl-items\">");
         w.push_buffer(default_impl_items);
         w.push_buffer(impl_items);
         close_tags.insert_str(0, "</div>");
+    }
     w.write_str(&close_tags);
 }