[bug] incorrect pathspec handling in git stash error message

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===== What did you do before the bug happened? (Steps to reproduce your issue)
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Here is how to reproduce the issue from scratch:
1. mkdir testrepo
2. cd testrepo
3. git init
4. touch testfile
5. git stash push testfile

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===== What did you expect to happen? (Expected behavior)
=====
Because 'testfile' is untracked, I expected an error message similar to this:
    testrepo $ git checkout testfile
    error: pathspec 'testfile' did not match any file(s) known to git

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===== What happened instead? (Actual behavior)
=====
This is what happens instead:
    testrepo $ git stash push testfile
    error: pathspec ':(prefix:0)testfile' did not match any file(s) known to git
    Did you forget to 'git add'?

===== ===== What's different between what you expected and what actually happened? ===== Looks like the magic prefix is handled incorrectly in git stash error messages.

========================= ========================= [System Info] git version: git version 2.47.1 cpu: arm64 no commit associated with this build sizeof-long: 8 sizeof-size_t: 8 shell-path: /bin/sh feature: fsmonitor--daemon libcurl: 8.6.0 zlib: 1.2.12 uname: Darwin 23.6.0 Darwin Kernel Version 23.6.0: Thu Sep 12 23:34:49 PDT 2024 compiler info: clang: 16.0.0 (clang-1600.0.26.4) libc info: no libc information available $SHELL (typically, interactive shell): /bin/zsh ========================= =========================