Ignore badly encoded std::variant IPC messages.

[Jean-Yves Avenard [:jya]]

Seen in 241407 with the ipc/pasteboard-write-custom-data.html test

It sends a rubbish buffer over IPC and ensure that the decoder doesn't crash.

When using the std::variant<> decoder, the decoder performs a recursive call in order to decode the property type like so:

std::variant<T1,T2,T3> obj;

decode<std::variant<T1,T2,T3...>>()
    read std::variant's index into i.
    VariantCoder<2, Types...>::decode(decoder, *i);
        VariantCoder<1, Types...>::decode(decoder, *i);
            VariantCoder<0, Types...>::decode(decoder, *i);

If the encoded value of i is nonsensical, we will get into calling VariantCoder<0, Types...>::decode(decoder, *i);

We should exit early when we read the value of I if it's greater than the number of types en variant can contain.

[Radar WebKit Bug Importer]

<rdar://problem/95016858>

[Jean-Yves Avenard [:jya]]

Pull request: https://github.com/WebKit/WebKit/pull/1472

[EWS]

Committed r295545 (251550@main): <https://commits.webkit.org/251550@main>

Reviewed commits have been landed. Closing PR #1472 and removing active labels.