Prevent warning when calling close() multiple times

Fixes #4

Author: thekid

ChangeLog.md

@@ -3,6 +3,10 @@ ZIP File support for the XP Framework ChangeLog
 
 ## ?.?.? / ????-??-??
 
+* Fixed issue #4: *Undefined property: [...]ZipFileOutputStream::$data*
+  when calling `close()` more than once.
+  (@thekid)
+
 ## 11.2.0 / 2025-08-16
 
 * Added compatibility with `xp-framework/math` version 10.0+ - @thekid

src/main/php/io/archive/zip/ZipFileOutputStream.class.php

@@ -84,6 +84,6 @@ public function close() {
       0
     );
     $this->writer->streamWrite($bytes);
-    unset($this->data);
+    $this->data= null;
   }
 }

src/test/php/io/archive/zip/unittest/ZipArchiveWriterTest.class.php

@@ -1,7 +1,7 @@
 <?php namespace io\archive\zip\unittest;
 
 use io\archive\zip\{ZipArchiveWriter, ZipDirEntry, ZipFile, ZipFileEntry};
-use io\streams\{MemoryInputStream, MemoryOutputStream};
+use io\streams\{MemoryInputStream, MemoryOutputStream, StreamTransfer};
 use lang\IllegalArgumentException;
 use test\{Assert, Expect, Test};
 
@@ -116,4 +116,19 @@ public function using_unicode_names() {
 
     Assert::equals(['関連事業調査.txt' => 'File contents'], $this->entriesWithContentIn($out, 'secret'));
   }
+
+  #[Test]
+  public function transferring_a_file() {
+    $out= new MemoryOutputStream();
+    $fixture= new ZipArchiveWriter($out);
+    $file= $fixture->add(new ZipFileEntry('test.txt'));
+
+    $transfer= new StreamTransfer(new MemoryInputStream('File contents'), $file->out());
+    $transfer->transferAll();
+    $transfer->close();
+
+    $fixture->close();
+
+    Assert::equals(['test.txt' => 'File contents'], $this->entriesWithContentIn($out));
+  }
 }