Fix Ui::add_visible sometimes leaving the Ui in a disabled state

Closes https://github.com/emilk/egui/issues/1436

CHANGELOG.md

@@ -23,6 +23,7 @@ NOTE: [`epaint`](epaint/CHANGELOG.md), [`eframe`](eframe/CHANGELOG.md), [`egui_w
 * Fixed ComboBoxes always being rendered left-aligned ([#1304](https://github.com/emilk/egui/pull/1304)).
 * Fixed ui code that could lead to a deadlock ([#1380](https://github.com/emilk/egui/pull/1380)).
 * Text is darker and more readable in bright mode ([#1412](https://github.com/emilk/egui/pull/1412)).
+* Fixed `Ui::add_visible` sometimes leaving the `Ui` in a disabled state. ([#1436](https://github.com/emilk/egui/issues/1436)).
 
 ### Removed 🔥
 * Removed the `single_threaded/multi_threaded` flags - egui is now always thread-safe ([#1390](https://github.com/emilk/egui/pull/1390)).

egui/src/ui.rs

@@ -1097,9 +1097,14 @@ impl Ui {
         if self.is_visible() && !visible {
             // temporary make us invisible:
             let old_painter = self.painter.clone();
+            let old_enabled = self.enabled;
+
             self.set_visible(false);
+
             let response = self.add(widget);
+
             self.painter = old_painter;
+            self.enabled = old_enabled;
             response
         } else {
             self.add(widget)