Don't leak temporary tuples in get_all()

[iustin]

Issue #35 found a bug in the tuple-to-list addition error handling. This should fix it.

[iustin]

Sigh, how the heck do I trigger a CI run on this pull request…

[codecov[bot]]

Codecov Report

Base: 87.77% // Head: 87.77% // No change to project coverage :thumbsup:

Coverage data is based on head (4f8165a) compared to base (c3466e7). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #36 +/- ## ======================================= Coverage 87.77% 87.77% ======================================= Files 1 1 Lines 499 499 ======================================= Hits 438 438 Misses 61 61 ``` | [Impacted Files](https://codecov.io/gh/iustin/pyxattr/pull/36?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Iustin+Pop) | Coverage Δ | | |---|---|---| | [xattr.c](https://codecov.io/gh/iustin/pyxattr/pull/36/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Iustin+Pop#diff-eGF0dHIuYw==) | `87.77% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Iustin+Pop). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Iustin+Pop)

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