Describe the bug

If a popup that is being shown is removed without calling Memory::close_popup, egui will think that the popup is still being shown, for example
Memory::any_popup_open() returns true.

Video of the problem:

You'd think the solution is to always call close_popup() but in some cases that's not practical, for example, the app stops rendering that part of the UI.

Proposed solution: clear Memory::popup at the end of a frame if is_popup_open was not called with the id of the current one (assume the popup was "abandoned"). Probably rename the function to something that reflects this behavior, e.g. retain_popup, check_and_keep_popup_open?

To Reproduce
Steps to reproduce the behavior:

1. Open a popup (e.g. color picker, drop-down, etc)
2. Without manually closing the popup, stop rendering it (i.e. don't hit that code path at all)
3. Memory::any_popup_open() is true

Expected behavior

Memory::any_popup_open() is false

Screenshots

Desktop (please complete the following information):

• Version 0.23.0