chtor: Fix `--reannounce-all` without `--no-cross-seed`

[ghost]

This fixes the following error when running chtor --reannounce-all without specifying --no-cross-seed:

Traceback (most recent call last):                                                   
  File "/home/nyuszika7h/.local/bin/chtor", line 8, in <module>
    sys.exit(run())                                                                  
  File "/home/nyuszika7h/.local/pipx/venvs/pyrosimple/lib/python3.10/site-packages/pyrosimple/scripts/chtor.py", line 400, in run
    MetafileChanger().run()                                                          
  File "/home/nyuszika7h/.local/pipx/venvs/pyrosimple/lib/python3.10/site-packages/pyrosimple/scripts/base.py", line 180, in run
    self.mainloop()                                                                  
  File "/home/nyuszika7h/.local/pipx/venvs/pyrosimple/lib/python3.10/site-packages/pyrosimple/scripts/chtor.py", line 306, in mainloop
    torrent["info"]["x_cross_seed"] = hashlib.md5(       
TypeError: Strings must be encoded before hashing        

[kannibalox]

Thanks!