Add stream test that loses buffer after cast

Co-authored-by: Arnaud Le Blanc <arnaud.lb@gmail.com>

Author: Girgias

ext/standard/tests/streams/stream_cast_loses_data.phpt

@@ -0,0 +1,162 @@
+--TEST--
+Casting a stream can lose data and needs to emit a warning
+--FILE--
+<?php
+$stream = popen('for i in $(seq 1 2000); do echo $i; done', 'r');
+sleep(2);
+
+// fills the read buffer with up to 8192 bytes
+fgets($stream);
+
+// cast $stream and read fd until eof. Print each line that was read, prefixed with "proc open stdin:"
+proc_open(
+    'sed "s/^/proc open stdin:/"',
+    [
+        0 => $stream,
+    ],
+    $pipes,
+);
+?>
+--EXPECTF--
+Warning: proc_open(): 8190 bytes of buffered data lost during stream conversion! in %s on line %d
+proc open stdin:
+proc open stdin:1861
+proc open stdin:1862
+proc open stdin:1863
+proc open stdin:1864
+proc open stdin:1865
+proc open stdin:1866
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