testlibrary: Initialize autofree variable to silence a compiler warning

[smcv]

As with commit 43085c0 "dir: Consistently initialize g_autofree variables", this is currently harmless because we never actually early-return or goto out of the region between declaration and initialization, but some compiler versions log a warning here anyway.

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[evelikov]

Don't know what the review process is, so fwiw:

Reviewed-by: Emil Velikov <[email protected]>

Side note: it might be beneficial to add bleeding edge distro into the mix (Arch or any other) which ships newer gcc/clang into the build matrix. Then one can also add -D werror=true to ensure new warnings don't silently creep-in.

Mind you this idea should be a separate follow-up PR, assuming maintainers see value in it in the first place.

[alexlarsson]

lgtm