Prevent error when close() called while writer already closed (#402)

tests/Spout/Writer/XLSX/WriterTest.php

@@ -194,6 +194,23 @@ class WriterTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals($firstSheet, $writer->getCurrentSheet(), 'The current sheet should be the first one.');
     }
 
+    /**
+     * @return void
+     */
+    public function testCloseShouldNoopWhenWriterIsNotOpened()
+    {
+        $fileName = 'test_double_close_calls.xlsx';
+        $this->createGeneratedFolderIfNeeded($fileName);
+        $resourcePath = $this->getGeneratedResourcePath($fileName);
+
+        $writer = WriterFactory::create(Type::XLSX);
+        $writer->close(); // This call should not cause any error
+
+        $writer->openToFile($fileName);
+        $writer->close();
+        $writer->close(); // This call should not cause any error
+    }
+
     /**
      * @return void
      */