Ensure @reader is nil before closing.

Author: ioquatix

lib/async/http/protocol/http2/connection.rb

@@ -101,6 +101,8 @@ def read_in_background(parent: Task.current)
 							ensure
 								# Don't call #close twice.
 								if @reader
+									@reader = nil
+									
 									self.close(error)
 								end
 							end