fix: do not mark call message as seen when declining a call

[link2xt]

When the message is marked as seen, an MDN (read receipt) is sent to self
and receiving such MDN marks all messages in the chat above the call message as noticed.
Calls may be declined from the notification, so user may decline a call
without ever seeing a call message in the chat.

Closes#8631

[hpk42]

I am afraid I don't quite get the overall scheme of how caller/callee and their multi-device setups are meant to land in consistent states including UI notifications/interactions. I filed an issue #8635 and is it not strictly related to this particular PR.

For this PR my main concern is that the second device of the Callee might be left with a "Missed call" notifcation if there is no self-MDN anymore. As far as i see, at receiving time, a stale-on-arrival call notifies via

core/src/calls.rs

Lines 368 to 372 in 3784b3e

	if call.is_incoming(){
	if call.is_stale(){
	let missed_call_str = stock_str::missed_call(self);
	call.update_text(self,&missed_call_str).await?;
	self.emit_incoming_msg(call.msg.chat_id, call_id);// notify missed call

and i don't see what removes that notification afterwards.

The accepted-call path should probably be handled before #8631 can be closed but it doesn't necessarily block this PR i guess.

[hpk42]

isn't this the same problem?

i guess there should be a helper that both declining and accept call use.

[hpk42]

This by itself does not send out anything, right?