…g ignore depth

This change makes sure that we are properly checking the ignored field
recursion depth in decIgnoreOpFor consistently. This prevents stack
exhaustion when attempting to decode a message that contains an
extremely deeply nested struct which is ignored.

Thanks to Md Sakib Anwar of The Ohio State University (anwar.40@osu.edu)
for reporting this issue.

Updates #69139
Fixes #69144
Fixes CVE-2024-34156

Change-Id: Iacce06be95a5892b3064f1c40fcba2e2567862d6
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/1440
Reviewed-by: Russ Cox <rsc@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
(cherry picked from commit f0a11f9b3aaa362cb1d05e095e3c8d421d4f087f)
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/1580
Reviewed-by: Tatiana Bradley <tatianabradley@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/611182
TryBot-Bypass: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>