Improve test

Ensure the filename is non existent indeed.

Author: weltling

ext/zip/tests/bug76524.phpt

@@ -7,7 +7,10 @@ if(!extension_loaded('zip')) die('skip');
 --FILE--
 <?php
 
-$filename = __DIR__ . '/nonexistent.zip';
+$i = 0;
+do {
+	$filename = __DIR__ . "/nonexistent" . ($i++) . ".zip";
+} while (file_exists($filename));
 
 $zip = new ZipArchive();
 $zip->open($filename, ZipArchive::CREATE | ZipArchive::OVERWRITE);