[BUG b4] Encoding issues with --auto-to-cc

["Duje Mihanović" <duje.mihanovic@skole.hr>]

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I decided to try using b4 to submit a patchset for adding Marvell PXA1908 ARM 
SoC support. Having enrolled an existing branch, I ran `b4 prep -c` and got 
the following error (this is with the -d switch added):

Collecting from: [PATCH v2 06/10] dt-bindings: clock: Add documentation for 
Marvell PXA1908
Running git --no-pager rev-parse --show-toplevel
Changing dir to /home/duje/code/linux
Running /home/duje/code/linux/scripts/get_maintainer.pl --nogit --nogit-
fallback --nogit-chief-penguins --norolestats --nol
Changing back into /home/duje/code/linux/Documentation/process
Traceback (most recent call last):
  File "/usr/bin/b4", line 33, in <module>
    sys.exit(load_entry_point('b4==0.12.3', 'console_scripts', 'b4')())
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/b4/command.py", line 360, in cmd
    cmdargs.func(cmdargs)
  File "/usr/lib/python3.11/site-packages/b4/command.py", line 76, in cmd_prep
    b4.ez.cmd_prep(cmdargs)
  File "/usr/lib/python3.11/site-packages/b4/ez.py", line 1994, in cmd_prep
    auto_to_cc()
  File "/usr/lib/python3.11/site-packages/b4/ez.py", line 1896, in auto_to_cc
    for tname, pairs in (('To', get_addresses_from_cmd(tocmd, msgbytes)),
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/b4/ez.py", line 948, in 
get_addresses_from_cmd
    addrs = out.strip().decode()
            ^^^^^^^^^^^^^^^^^^^^
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x87 in position 201: 
invalid start byte

I suspected that using an existing branch instead of creating a new one could 
have caused this problem, so I unzipped a 6.5-rc2 tarball into /tmp, 
initialized a Git repository there and used `git am` to apply initially only 
the patch 06/10 which was causing issues in the other repository and ran `b4 
prep -c` again. This time b4 was able to collect the addresses without issues, 
but then I tried `git am`ing the whole set into the /tmp repository and this 
time `b4 prep -c` failed with the same error on the same patch.

Steps to reproduce:
    - Checkout Linux 6.5-rc2
    - Run `b4 prep -F "<20230721210042.21535-1-duje.mihanovic@skole.hr>" -n 
<any branch name>`
    - Run `b4 prep -c`

--
Regards,
Duje

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