Process Comments in Sylk File (#2277)

Fixes issue #2276.

tests/PhpSpreadsheetTests/Reader/Slk/SlkCommentsTest.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Slk;
+
+use PhpOffice\PhpSpreadsheet\Reader\Slk;
+
+class SlkCommentsTest extends \PHPUnit\Framework\TestCase
+{
+    public function testComments(): void
+    {
+        $testbook = 'tests/data/Reader/Slk/issue.2276.slk';
+        $reader = new Slk();
+        $spreadsheet = $reader->load($testbook);
+        $sheet = $spreadsheet->getActiveSheet();
+        $comments = $sheet->getComments();
+        self::assertCount(2, $comments);
+        self::assertArrayHasKey('A1', $comments);
+        self::assertArrayHasKey('B2', $comments);
+        self::assertSame("Zeratul:\nEn Taro Adun!", $sheet->getComment('A1')->getText()->getPlainText());
+        self::assertSame("Arthas:\nFrostmourne Hungers.", $sheet->getComment('B2')->getText()->getPlainText());
+        $spreadsheet->disconnectWorksheets();
+    }
+}

tests/data/Reader/Slk/issue.2276.slk

@@ -0,0 +1,10 @@
+ID;PWXL;N;E
+P;PGeneral
+F;P0;DG0G10;M320
+B;Y3;X1;D0 0 9 0
+C;Y1;X1;AZeratul: :En Taro Adun!
+C;Y2;X2;AArthas: :Frostmourne Hungers.
+C;Y1;X1;K1
+C;Y1;X2;K2
+C;Y2;X1;K3
+E