on chat deletion, check ongoing calls and webxdc widgets

[r10s]

see comments at #3048 (comment) and #3048 (comment)

if need to scan all messages of a chat for that, it is unclear if that is worth the effort - and the performance cost. esp. as it seems uncommon to have a chat that is that important to put webxdc onto the widget - and then just delete it.

alternative may be to leave orphans in the widget and remove them once trying to be tapped. this seems to be useful anyways. maybe it is already the case.

for calls, this seems even more rare. not sure if we want to do anything about that but making sure, nothing crashes.

[Amzd]

I have just found out that we can't even remove the entries from the system Phone app retrospectively. We can block them from showing up there but not remove them afterwards.

[r10s]

maybe it is just fine to do nothing for the calls in the system Phone app, but making sure, nothing crashes when tapping