[Bug] Cosmic Session panic when stacking window

[KAIYOHUGO]

The cosmic session will panic if using stacking window in some way.

below is panic log,

cosmic-session[3710]: thread 'main' panicked at 'failed to kill program: Custom { kind: InvalidInput, error: "invalid argument: can't kill an exited process" }': /build/cosmic-session-wdYi53/cosmic-session-0.1.0~1733496467~22.04~78316ba/vendor/launch-pad/src/lib.rs:399
                                              0: <unknown>
                                              1: <unknown>
                                              2: <unknown>
                                              3: <unknown>
                                              4: <unknown>
                                              5: <unknown>
                                              6: <unknown>
                                              7: <unknown>
                                              8: <unknown>
                                              9: <unknown>
                                             10: <unknown>
                                             11: <unknown>
                                             12: <unknown>
                                             13: <unknown>
                                             14: <unknown>
                                             15: <unknown>
                                             16: <unknown>
                                             17: <unknown>
                                             18: <unknown>
                                             19: <unknown>
                                             20: <unknown>
                                             21: __libc_start_call_main
                                                        at ./csu/../sysdeps/nptl/libc_start_call_main.h:58:16
                                             22: __libc_start_main_impl
                                                        at ./csu/../csu/libc-start.c:392:3
                                             23: <unknown>

The way to reproduce as the video show

crash.mp4

If toggle window stacking first then maximize that window, it will cause any new open window appear twice on both left and right side.

If maximize window first then toggle window stacking , it will bug out (cannot un-maximize) when open new window and will panic if you try to close it.