TestArchive doesn't handle invalid offsets correctly

从 src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs 中 TestArchive 循环附近以及 issue 所引用的 entry.Offset 处理开始。跟踪无效偏移量如何到达 System.IO，然后添加回归测试覆盖，表明 TestArchive 会报告无效条目，并在 TestStrategy.FindAllErrors 下继续测试其他条目。

Describe the bug

Entry header offsets are not checked for validity before trying to seek to them in the stream. Invalid offsets (i.e. <0) cause InvalidArgumentExceptions to be thrown from inside System.IO code, which are not caught in the existing ZipException handlers. They bubble up and cause the entire archive to fail validation with a cryptic "The parameter is incorrect - {filename}" message.

Reproduction Code

using ICSharpCode.SharpZipLib.Zip;

namespace TestArchive
{
    internal class Program
    {
        static void Main(string[] args)
        {
            string zipPath = @"C:\temp\test.zip";
            using var stream = System.IO.File.OpenRead(zipPath);
            using var zip = new ZipFile(stream);
            bool isValid = zip.TestArchive(false, TestStrategy.FindAllErrors, ZipTestResultHandler); 
            if (!isValid)
            {
                throw new ArgumentException("Zip file is invalid!");
            }
        }

        static void ZipTestResultHandler(TestStatus status, string message)
        {
            if (status.Entry != null && !status.EntryValid && !string.IsNullOrEmpty(message))
            {
                Console.WriteLine(status.Entry.ZipFileIndex + ": " + status.Entry.Name);
                Console.WriteLine(message);
            }
        }
    }
}

Steps to reproduce

1. Get a zip file with an entry whose Offset is negative (this is generally an invalid state and I don't know how to create one like this)
2. Call TestArchive() and pass in a ZipTestResultHandler to get the test results

Expected behavior

I expect each individual entry with an invalid offset/header to be reported on (assuming TestStrategy.FindAllErrors is specified)

Operating System

Windows

Framework Version

Other

Tags

ZIP

Additional context

entry.Offset not being checked for > 0: https://github.com/icsharpcode/SharpZipLib/blob/master/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs#L1184

Where the InvalidArgumentException from deep in System.IO gets caught outside the while loop (additional entries are not tested): https://github.com/icsharpcode/SharpZipLib/blob/master/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs#L1144