event_loop: correctly use prepare_read()

[elinorbgr]

Fixes #212

@Molytho can you confirm this one is correct for good?

[Molytho]

It works perfectly fine 👍.

One last thing:
Maybe replace this

client-toolkit/src/event_loop.rs

Lines 99 to 117 in 3c87c00

	loop {
	let ret = callback((), queue);
	match ret {
	Ok(0) => {
	// no events were dispatched even after reading the socket,
	// nothing more to do, stop here
	*read_guard = queue.prepare_read();
	break;
	}
	Ok(_) => {
	*read_guard = queue.prepare_read();
	continue;
	}
	Err(e) => {
	// in case of error, forward it and fast-exit
	return Err(e);
	}
	}
	}

with that

client-toolkit/src/event_loop.rs

Lines 167 to 177 in 3c87c00

	loop {
	match self.queue.prepare_read() {
	Some(guard) => {
	self.read_guard = Some(guard);
	break;
	}
	None => {
	callback((), &mut self.queue)?;
	}
	}
	}

because prepare_read is no longer needed in the Ok(_) => { ... } path and because prepare_read can fail in the Ok(0) => { ... } when something is read in between of callback and prepare_read (I know that's very unlikely to ever happen but when it happens once it's impossible to track down)

[elinorbgr]

Ah yes, good point!

[Molytho]

It works. I think it's ready to be commited