Fix sender_double_check regression

introduce from fb4305a, mistaken SINK condition

Which makes wake() always be retry Next

test_basic_multi_tx_async_1_rx_blocking::case_8 (1000 senders) >60s

Author: frostyplanet

src/shared.rs

@@ -177,9 +177,9 @@ impl<F: Flavor> ChannelShared<F> {
                 return self.senders.cancel_reuse_waker(o_waker, WakerState::Done);
             } else {
                 let state = if SINK {
-                    self.senders.commit_waiting(&o_waker)
+                    WakerState::Init as u8
                 } else {
-                    WakerState::Waiting as u8
+                    self.senders.commit_waiting(&o_waker)
                 };
                 if self.is_rx_closed() {
                     return WakerState::Closed as u8;

src/waker_registry.rs

@@ -378,6 +378,8 @@ impl<P: Copy> RegistryMulti<P> {
                         }
                     } else if state == WakerState::Closed as u8 {
                         return Some(Poll::Ready(()));
+                    } else {
+                        panic!("state: impossible for async {:?}", state);
                     }
                 }
             }