Ensure upgrade and tunnel responses correctly exit the request loop.

lib/async/http/protocol/http1/server.rb

@@ -71,7 +71,8 @@ def each(task: Task.current)
 										request = nil unless request.body
 										response = nil
 
-										body.call(stream)
+										# We must return here as no further request processing can be done:
+										return body.call(stream)
 									else
 										write_response(@version, response.status, response.headers)
 
@@ -82,7 +83,8 @@ def each(task: Task.current)
 											request = nil unless request.body
 											response = nil
 
-											body.call(stream)
+											# We must return here as no further request processing can be done:
+											return body.call(stream)
 										else
 											head = request.head?
 											version = request.version