Crash when pressing back button

[rfc2822]

Steps to reproduce:

• Preparation: add a subscription, close ICSx⁵
• Open subscription list
• Edit a subscription (EditCalendarActivity)
• Press back button

The app then crashes in the Emulator (Android 12).

I also don't know if we have to add

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU)
            onBackInvokedDispatcher.registerOnBackInvokedCallback(
                OnBackInvokedDispatcher.PRIORITY_DEFAULT,
            ) { handleOnBackPressed() }
        else
            onBackPressedDispatcher.addCallback { handleOnBackPressed() }

to every (?) activity, looks a bit much. In doubt I'd just ignore this Android 14 back button thing and keep things as simple as possible.

[ArnyminerZ]

We could add it to the other activities as well, but I don't know if it's necessary. We can use the AndroidX library and just have this:

onBackPressedDispatcher.addCallback(object : OnBackPressedCallback(true) {
    override fun handleOnBackPressed() { /* HANDLE BACKPRESS */ }
})

Found it in this codelab.