Breakage on latest master

[karolyi]

Nicotine+ Version: 3.3.0.dev1
GTK Version: 3.24.33
Python Version: 3.8.13 (default, Mar 26 2022, 01:14:17)
[Clang 11.0.1 (git@github.com:llvm/llvm-project.git llvmorg-11.0.1-0-g43ff75f2c

Type: <class 'AttributeError'>
Value: 'NoneType' object has no attribute 'conn_type'
Traceback:   File "/home/user/nicotine-plus/pynicotine/gtkgui/frame.py", line 1853, in _on_critical_error_threading
    raise args.exc_value
  File "/usr/local/lib/python3.8/threading.py", line 932, in _bootstrap_inner
    self.run()
  File "/home/user/nicotine-plus/pynicotine/slskproto.py", line 2259, in run
    self.process_conn_input(sock, conn_obj)
  File "/home/user/nicotine-plus/pynicotine/slskproto.py", line 1929, in process_conn_input
    self.process_peer_init_input(conn_obj, conn_obj.ibuf)
  File "/home/user/nicotine-plus/pynicotine/slskproto.py", line 1482, in process_peer_init_input
    self.close_connection(self._conns, conn_obj.sock)
  File "/home/user/nicotine-plus/pynicotine/slskproto.py", line 1144, in close_connection
    conn_type = conn_obj.init.conn_type