Fix segfault in wrapper error log mechanism when errors are logged on

Fix segfault in wrapper error log mechanism when errors are logged on
second and subsequent events.
Implement very simple recursion protection for user streams written
like this:
class urlEncodeStream {
    var $fp = NULL;

    function stream_open($path, $mode, $options, &$opened_path)
    {
        $this->fp = fopen($path, $mode); // <-- this recurses infinitely
        return is_resource($this->fp);
    }
}

file_register_wrapper('urlencode', 'urlEncodeStream');
$fp = fopen('urlencode:///tmp/outputfile.txt', 'w');

Noticed by: Yasuo.