Fix deadlock in remote protocol.

The `TransportConnectionWrapper` producer-consumer queue was deadlocking due to
`_signal` getting set to `null` while a worker was still waiting for it. Spoke
with @kekekeks who suggested this fix.

src/Avalonia.Remote.Protocol/TransportConnectionWrapper.cs

@@ -64,7 +64,7 @@ namespace Avalonia.Remote.Protocol
         
         public Task Send(object data)
         {
-            var tcs = new TaskCompletionSource<int>();
+            var tcs = new TaskCompletionSource<int>(TaskCreationOptions.RunContinuationsAsynchronously);
             lock (_lock)
             {
                 if (!_workerIsAlive)
@@ -79,8 +79,9 @@ namespace Avalonia.Remote.Protocol
                 });
                 if (_signal != null)
                 {
-                    _signal.SetResult(0);
+                    var signal = _signal;
                     _signal = null;
+                    signal.SetResult(0);
                 }
             }
             return tcs.Task;
@@ -98,4 +99,4 @@ namespace Avalonia.Remote.Protocol
             remove => _onException.Remove(value);
         }
     }
-}
+}