fix warning when open xlsx file with thumbnail

src/PhpSpreadsheet/Reader/Xlsx.php

@@ -149,6 +149,7 @@ private function loadZipNonamespace(string $filename, string $ns): SimpleXMLElem
 
     private const REL_TO_MAIN = [
         Namespaces::PURL_OFFICE_DOCUMENT => Namespaces::PURL_MAIN,
+        Namespaces::THUMBNAIL => '',
     ];
 
     private const REL_TO_DRAWING = [

src/PhpSpreadsheet/Reader/Xlsx/Namespaces.php

@@ -14,6 +14,8 @@ class Namespaces
     // This one used in Reader\Xlsx\Properties
     const CORE_PROPERTIES2 = 'http://schemas.openxmlformats.org/package/2006/metadata/core-properties';
 
+    const THUMBNAIL = 'http://schemas.openxmlformats.org/package/2006/relationships/metadata/thumbnail';
+
     const THEME = 'http://schemas.openxmlformats.org/package/2006/relationships/theme';
 
     const COMPATIBILITY = 'http://schemas.openxmlformats.org/markup-compatibility/2006';

tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2516Test.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
+use PHPUnit\Framework\TestCase;
+
+class Issue2516Test extends TestCase
+{
+    /**
+     * @var string
+     */
+    private static $testbook = 'tests/data/Reader/XLSX/issue.2516b.xlsx';
+
+    public function testPreliminaries(): void
+    {
+        $file = 'zip://';
+        $file .= self::$testbook;
+        $file .= '#docProps/thumbnail.wmf';
+        $data = file_get_contents($file);
+
+        // confirm that file exists
+        self::assertNotFalse($data, 'thumbnail.wmf not exists');
+
+        $file = 'zip://';
+        $file .= self::$testbook;
+        $file .= '#_rels/.rels';
+        $data = file_get_contents($file);
+        // confirm that file contains expected namespaced xml tag
+        if ($data === false) {
+            self::fail('Unable to read file .rels');
+        } else {
+            self::assertStringContainsString('Type="http://schemas.openxmlformats.org/package/2006/relationships/metadata/thumbnail" Target="docProps/thumbnail.wmf"', $data);
+        }
+    }
+
+    public function testIssue2516a(): void
+    {
+        $filename = self::$testbook;
+        $reader = new Xlsx();
+        $names = $reader->listWorksheetNames($filename);
+        $expected = ['Sheet1'];
+        self::assertSame($expected, $names);
+    }
+
+    public function testIssue2516b(): void
+    {
+        $filename = self::$testbook;
+        $reader = new Xlsx();
+        $infos = $reader->listWorksheetInfo($filename);
+        $expected = [
+            [
+                'worksheetName' => 'Sheet1',
+                'lastColumnLetter' => 'B',
+                'lastColumnIndex' => 1,
+                'totalRows' => '6',
+                'totalColumns' => 2,
+            ],
+        ];
+        self::assertSame($expected, $infos);
+    }
+}