Fix issue with locating package parts in files that contain absolute …

…relation paths.

source/Sylvan.Data.Excel.Tests/CustomTests.cs

@@ -5,6 +5,30 @@ namespace Sylvan.Data.Excel;
 
 public class CustomTests
 {
+
+	[Fact]
+	public void BadSlash()
+	{
+		// This file contains package relations that use absolute rooted paths instead of relative paths.
+		// "/xl/workbook.xml" vs "xl/workbook.xml"
+		// This was causing the issues with the code that locates the package parts 
+		TestSlash("Data/sample_file_bad.xlsx");
+	}
+
+	[Fact]
+	public void GoodSlash()
+	{
+		TestSlash("Data/sample_file_good.xlsx");
+	}
+
+	void TestSlash(string file)
+	{
+		using var reader = ExcelDataReader.Create(file);
+
+		var b = reader.TryOpenWorksheet("MasterInvoice_Detailed_XLSX");
+		Assert.True(b);
+	}
+
 	[Fact]
 	public void InlineString()
 	{

source/Sylvan.Data.Excel/Xlsx/XlsxWorkbookReader.cs

@@ -193,10 +193,7 @@ private protected override ref readonly FieldInfo GetFieldValue(int ordinal)
 	private protected override bool OpenWorksheet(int sheetIdx)
 	{
 		var sheetName = sheetInfos[sheetIdx].Part;
-		// the relationship is recorded as an absolute path
-		// but the zip entry has a relative name.
-		sheetName = sheetName.TrimStart('/');
-		var sheetPart = package.GetEntry(sheetName);
+		var sheetPart = package.FindEntry(sheetName);
 		if (sheetPart == null)
 			return false;