fix bug issue #8 - Error if the file is empty

tests/PhpZip/ZipFileTest.php

@@ -1,4 +1,5 @@
 <?php
+
 namespace PhpZip;
 
 use PhpZip\Exception\ZipAuthenticationException;
@@ -1811,6 +1812,19 @@ class ZipFileTest extends ZipTestCase
         self::assertTrue($result);
     }
 
+    public function testEmptyContents()
+    {
+        $zipFile = new ZipFile();
+        $contents = '';
+        $zipFile->addFromString('file', $contents);
+        $zipFile->saveAsFile($this->outputFilename);
+        $zipFile->close();
+
+        $zipFile->openFile($this->outputFilename);
+        self::assertEquals($zipFile['file'], $contents);
+        $zipFile->close();
+    }
+
     /**
      * Test support ZIP64 ext (slow test - normal).
      * Create > 65535 files in archive and open and extract to /dev/null.