fix bug EventBus::broadcast

[songgaoye]

Closes: #XXX

hermes/crates/relayer/src/event/bus.rs

Lines 28 to 42 in 5e78a42

	pub fn broadcast(&mut self, value: T)
	where
	T: Clone,
	{
	let mut disconnected = Vec::new();
	for (idx, tx) in self.txs.iter().enumerate() {
	// TODO: Avoid cloning when sending to last subscriber
	if let Err(channel::SendError(_)) = tx.send(value.clone()) {
	disconnected.push(idx);
	}
	}
	// Remove all disconnected subscribers
	for idx in disconnected {

The original code has a correctness bug:

Collecting indices [0, 2, 5] to remove
After remove(0), index 2 becomes 1, index 5 becomes 4
Removes wrong elements!

Description

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• Added changelog entry, using unclog.
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