Description:
------------
imap_mail_compose() corrupts passed $envelope parameter, even passed 
indirectly - check $headers and $this->headers used in sample code.

All address headers (from, to, cc, bcc, reply_to etc.) are changed and 
variable can't be passed to imap_mail_compose() next time, beacause 
function produces notice and wrong mail headers:
From: Asdf@NO HOST, UNEXPECTED_DATA_AFTER_ADDRESS@.SYNTAX-ERROR.

Any modification (uncomment line in sample) to variable 
prevents changes to $this->headers, but $headers is still being 
modified.

Reproduce code:
---------------
class test {
    protected $headers = array("from" => "Asdf Qwer <asdf@qwer.invalid>");
    protected $body = array(array(
        "type" => TYPETEXT,
        "subtype" => "plain",
        "contents.data" => "test message",
    ));
    protected function getHeaders() {
        return $this->headers;
    }
    public function compose() {
        $headers = $this->getHeaders();
        //$headers["from"] .= ""; // uncomment to fix
        var_dump($this->headers["from"]);
        imap_mail_compose($headers, $this->body);
        var_dump($this->headers["from"]);
    }
}
$test = new test();
$test->compose();

Expected result:
----------------
string(29) "Asdf Qwer <asdf@qwer.invalid>"
string(29) "Asdf Qwer <asdf@qwer.invalid>"

Actual result:
--------------
string(29) "Asdf Qwer <asdf@qwer.invalid>"
string(29) "Asdf Qwer<asdf@qwer.invalid>"

One space is replaced by 0x00.