Another Undefined Index in Xls Reader (#2470)

Fix #2463. These continue to dribble in regularly.

src/PhpSpreadsheet/Reader/Xls.php

@@ -6941,7 +6941,7 @@ class Xls extends BaseReader
                 // offset: 1; size: 2; one-based index to definedname record
                 $definedNameIndex = self::getUInt2d($formulaData, 1) - 1;
                 // offset: 2; size: 2; not used
-                $data = $this->definedname[$definedNameIndex]['name'];
+                $data = $this->definedname[$definedNameIndex]['name'] ?? '';
 
                 break;
             case 0x24:    //    single cell reference e.g. A5

tests/PhpSpreadsheetTests/Reader/Xls/Issue2463Test.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xls;
+use PHPUnit\Framework\TestCase;
+
+class Issue2463Test extends TestCase
+{
+    public function testNoUnknownIndexNotice(): void
+    {
+        // Unknown index notice when loading
+        $filename = 'tests/data/Reader/XLS/issue.2463.xls';
+        $reader = new Xls();
+        $spreadsheet = $reader->load($filename);
+        $sheet = $spreadsheet->getActiveSheet();
+        self::assertSame('bol.com bestellingen', $sheet->getTitle());
+        $spreadsheet->disconnectWorksheets();
+    }
+}