Fix OSError in ProxyListener.py

[TakahiroHaruyama]

I enabled the Static_CA setting and set HTTPListener443’s Hidden option to True to test TLS MitM (dynamically generating certificates based on the destination), but I encountered the following error.

Exception occurred during processing of request from ('172.30.0.129', 38278)
Traceback (most recent call last):
  File "/usr/lib/python3.12/socketserver.py", line 692, in process_request_thread
    self.finish_request(request, client_address)
  File "/usr/lib/python3.12/socketserver.py", line 362, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python3.12/socketserver.py", line 761, in __init__
    self.handle()
  File "/opt/venv/lib/python3.12/site-packages/fakenet/listeners/ProxyListener.py", line 245, in handle
    remote_sock.setblocking(0)
OSError: [Errno 9] Bad file descriptor

So I fixed the code.
Reference: https://migawari-iv.hatenablog.com/entry/2024/05/06/223200 (in Japanese)