[3.7] bpo-31047: Fix ntpath.abspath for invalid paths (GH-8544)

[miss-islington]

(cherry picked from commit d2e902e)

Co-authored-by: Franz Wöllert [email protected]

https://bugs.python.org/issue31047

[the-knights-who-say-ni]

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[miss-islington]

@mansenfranzen and @zooba: Backport status check is done, and it's a success ✅ .