After closing for error do not keep alive

Raise a StopIteration rather than returning so that the keep-alive
loop is terminated. If gunicorn has closed the socket there is no
sense in trying to read another request and it may cause spurious
EBADF errors to try.

gunicorn/workers/async.py

@@ -113,7 +113,7 @@ class AsyncWorker(base.Worker):
                     sock.close()
                 except socket.error:
                     pass
-                return
+                raise StopIteration()
             raise
         finally:
             try:

gunicorn/workers/sync.py

@@ -152,8 +152,7 @@ class SyncWorker(base.Worker):
                     client.close()
                 except socket.error:
                     pass
-
-                return
+                raise StopIteration()
             # Only send back traceback in HTTP in debug mode.
             self.handle_error(req, client, addr, e)
             return