[Toybox] Update chsh patch

[amichaelc]

I had a few (3 maybe?) system calls where I got the error checking backwards, so I fixed those. I also realized I forgot to format the code with the 80 character thing, so I shortened a bunch of lines.

The command works fine except for when I request a shell of 15+ characters (such as /usr/bin/xonsh), in which case it segfaults. I'm still working on this, but I think the string is too long for the passwd struct (which wouldn't explain why `update_passwd("/etc/passwd", user, NULL)` is failing).

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