debug/buildinfo: avoid nil defererence for invalid XCOFF
I've made it return 0 following what the other DataStart implementation
do when they do not found the section.
Fixes #52718
Change-Id: I44292fed15bb21b9aba712ad15ed74e0ce231b5a
GitHub-Last-Rev:
081a35ebec9b94c0fa6a1347806d84111e58210a
GitHub-Pull-Request: golang/go#52722
Reviewed-on: https://go-review.googlesource.com/c/go/+/404254
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: David Chase <drchase@google.com>