fixup! Support for passing Connection::Blocked frames to downstream c…

…lients

src/amqproxy/upstream.cr

@@ -135,12 +135,14 @@ module AMQProxy
       end
     end
 
-    private def send_to_all_clients(frame : AMQ::Protocol::Frames::Connection)
+    private def send_to_all_clients(frame : AMQ::Protocol::Frame::Connection)
       Log.debug { "Sending broadcast frame to all client connections" }
       clients = Set(Client).new
       @channels_lock.synchronize do
         @channels.each_value do |downstream_channel|
-          clients << downstream_channel.client
+          if dc = downstream_channel
+            clients << dc.client
+          end
         end
       end
       clients.each do |client|