Add a test case for zlib.deflate

Cf. <https://bugs.php.net/48725#1351085255>.

Author: cmb69

ext/zlib/tests/bug48725_2.phpt

@@ -0,0 +1,15 @@
+--TEST--
+Bug #48725 (Support for flushing in zlib stream)
+--SKIPIF--
+<?php
+if (!extension_loaded('zlib')) die('skip zlib extension not available');
+?>
+--FILE--
+<?php
+$stream = fopen('data://text/plain;base64,' . base64_encode('Foo bar baz'), 
+'r');
+stream_filter_append($stream, 'zlib.deflate', STREAM_FILTER_READ);
+print bin2hex(stream_get_contents($stream));
+?>
+--EXPECT--
+72cbcf57484a2c02e22a00000000ffff0300