procfs: Swallow InvalidFileFormat when parsing ns/pid, fixing invocation as unprivileged user

[Flowdalic]

Summary:

When running below as an unprivileged user, reading /proc/1/ns/pid may yield an empty string due to permissions, resulting in an InvalidFileFormat error instead of an IoError. Fix below invocations as unprivileged user by ignoring InvalidFileFormat in read_all_pid_info_from_path (similar to EACCES) so that execution does not abort early when encountering an inaccessible process namespace.

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