gh-133590: ensure that TableEntry.linenumber_borrow is initialized

[ljfp]

Since the author decided to initialize filename_borrow to NULL, I think that linenumber_borrow should also be initialized (likely to 0).

In its current state it could become an issue in the report_leak() function if for some reason entry->linenumber_borrow = linenumber; fails to be executed and then linenumber_borrow is accessed when filename_borrow is non-NULL. I'm not sure if this code path is possible at all, but initializing linenumber_borrow shouldn't have any side-effects.

If this was left intentionally uninitialized for some reason, it would be a good idea to close this PR and open another one documenting the motive behind leaving it like this.

Also, stackrefs.c had a blank line at the beginning of the file (!!); I took the liberty to remove it.

• Issue: Initialize the linenumber_borrow field of the TableEntry struct #133590

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[picnixz]

One could argue that it's not an undefined behavior as linenumber_borrow will always be set to something before it's read but accessing it while uninitialized is indeed UB.

[picnixz]

CI seems stuck. I'll close/reopen your PR.

[miss-islington-app]

Thanks @ljfp for the PR, and @picnixz for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-133872 is a backport of this pull request to the 3.14 branch.