[BUG] typo DWIMery with alias broken (cd to random dir)

Hi there,

with current next (989ee58 plus local additions) it seems that typo
DWIMery with aliases is broken, see below.

It appears that the typo DWIMery is broken only when there is a unique
automatic DWIM substitution for a mistyped alias.

I haven't bisected yet, but I suspect this to be related to recent
changes regarding the environment in which commands/aliases are started
(though this happens without extra work trees), so I'm cc'ing an expert
in that area. Funny, though, that my user name shows up...

I think the reason is that git.c's handle_alias() (or something else)
calls restore_env() multiple times, and restore_env frees orig_cwd such
that subsequent restore_env(0) with external_alias=0 tries to cd to a
random location.

I have no idea whether orig_cwd=0 after freeing or something else would
be the proper fix.

Michael

LANG=C git sss
WARNING: You called a Git command named 'sss', which does not exist.
Continuing under the assumption that you meant 'ss'
in 2.0 seconds automatically...
fatal: could not move to git@drmicha.warpmail.net: No such file or directory
[mjg@skimbleshanks git]✗ LANG=C git ss
## HEAD (no branch)
?? a
?? a.patch
?? c2d.sh
[mjg@skimbleshanks git]✓ LANG=C git statu -sb
git: 'statu' is not a git command. See 'git --help'.

Did you mean one of these?
        status
        stage
        stash
[mjg@skimbleshanks git]✗ LANG=C git statuss -sb
WARNING: You called a Git command named 'statuss', which does not exist.
Continuing under the assumption that you meant 'status'
in 2.0 seconds automatically...
## HEAD (no branch)
?? a
?? a.patch
?? c2d.sh