Fix test case

As of PHP 7.3.0, unlinking files with open handles is possible on
Windows, but these file entries are still blocked until all open
handles are closed.  Since this test doesn't require to write to the
same file, we use three separate files.

We also add the missing skip check for XMLReader.

Author: cmb69

ext/xmlwriter/tests/bug79029.phpt

@@ -1,29 +1,31 @@
 --TEST--
 #79029 (Use After Free's in XMLReader / XMLWriter)
 --SKIPIF--
-<?php if (!extension_loaded("xmlwriter")) print "skip"; ?>
+<?php 
+if (!extension_loaded("xmlwriter")) print "skip xmlwriter extension not available";
+if (!extension_loaded("xmlreader")) print "skip xmlreader extension not available";
+?>
 --FILE--
 <?php
 $x = array( new XMLWriter() );
-$x[0]->openUri("bug79029.txt");
+$x[0]->openUri("bug79029_1.txt");
 $x[0]->startComment();
-@unlink("bug79029.txt");
 
 $x = new XMLWriter();
-$x->openUri("bug79029.txt");
+$x->openUri("bug79029_2.txt");
 fclose(@end(get_resources()));
-@unlink("bug79029.txt");
 
-file_put_contents("bug79029.txt", "a");
+file_put_contents("bug79029_3.txt", "a");
 $x = new XMLReader();
-$x->open("bug79029.txt");
+$x->open("bug79029_3.txt");
 fclose(@end(get_resources()));
-@unlink("bug79029.txt");
 ?>
 okey
 --CLEAN--
 <?php
-@unlink("bug79029.txt");
+@unlink("bug79029_1.txt");
+@unlink("bug79029_2.txt");
+@unlink("bug79029_3.txt");
 ?>
 --EXPECTF--
 Warning: fclose(): %d is not a valid stream resource in %sbug79029.php on line %d