Ensure the ping interval waker is registered

When an interval is ready it does not need to register its internal
waker, leading to the future not being polled anymore if no data is
received from the connection.

The fix is pretty simple, and it should never cause any problem unless
the interval duration is very close to zero, which will probably cause
strange issues anyway.

async-nats/src/lib.rs

@@ -487,7 +487,10 @@ impl ConnectionHandler {
             ///   [`Self::receiver`] was closed, so there's nothing
             ///   more for us to do than to exit the client.
             fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-                if self.handler.ping_interval.poll_tick(cx).is_ready() {
+                // We need to be sure the waker is registered, therefore we need to poll until we
+                // get a `Poll::Pending`. With a sane interval delay, this means that the loop
+                // breaks at the second iteration.
+                while self.handler.ping_interval.poll_tick(cx).is_ready() {
                     if let Poll::Ready(exit) = self.ping() {
                         return Poll::Ready(exit);
                     }