Prevent too deep recursion

[sugar700]

No description provided.

[dtolnay]

Thanks!

[Shnatsel]

Is it possible to backport this to 0.3.x series? According to crates.io stats, half of the recent downloads of rust-yaml are in the 0.3.x.

If this fix is already backported, please let me know and I'll update the security advisory.

[sugar700]

@Shnatsel Most of the rust-yaml downloads are due to clap, which isn't really affected by this issue, making this mostly unimportant.

[Shnatsel]

There is a total of 165 crates on crates.io currently affected without a semver-compatible upgrade path, according to crates-audit. So it might not be as unimportant as it seems.

[Shnatsel]

Here's the list of affected crates, without crates depending on clap, sorted by recent download count: https://ncry.pt/p/vzOn#8UqV4ktfnn67-ReSMfvj-xjFZQq1wdDh3uUzK8AhxBk
That's 51 crates, nothing really critical at the top of the list as far as I can tell.