Description:
------------
iconv_mime_decode_headers function is skipping headers when '=?' is present in the subject. 

For example if the subject header of a mime message is : 
Subject: Reply Is? white side-LED =? in Help

Then the rest of the headers after subject like content-type, date etc are not returned. Similar bug is filed https://bugs.php.net/bug.php?id=52941 but in the above mentioned example the subject is not encoded. 

My php version is 5.3.3 and the issue is reproducible in 5.3.20 and 5.4.10. 

Test script:
---------------
<?php
$headers = 'From: "xyz" <xyz@xyz.com>
To: <xyz@xyz.com>
Subject: Reply Is? white side-LED =? in Help
Date: Sat, 22 Dec 2012
Message-ID: <006f01cde00e$d9f79da0$8de6d8e0>
MIME-Version: 1.0
Content-Type: multipart/alternative;
	boundary="----=_NextPart_000_0070_01CDE03C.F3AFD9A0"
X-Mailer: Microsoft Office Outlook 12.0
Thread-Index: Ac3gDtcH2huHjzYcQVmFJPPoWjJogA==
Content-Language: en-us

';
$headers = iconv_mime_decode_headers($headers, ICONV_MIME_DECODE_CONTINUE_ON_ERROR);
print_r($headers);
?>

Expected result:
----------------
Array
(
    [From] => "xyz" <xyz@xyz.com>
    [To] => <xyz@xyz.com>
    [Subject] => Reply Is? white side-LED =? in Help
    [Date] => Sat, 22 Dec 2012
    [Message-ID] => <006f01cde00e$d9f79da0$8de6d8e0>
    [MIME-Version] => 1.0
    [Content-Type] => multipart/alternative; boundary="----=_NextPart_000_0070_0
1CDE03C.F3AFD9A0"
    [X-Mailer] => Microsoft Office Outlook 12.0
    [Thread-Index] => Ac3gDtcH2huHjzYcQVmFJPPoWjJogA==
    [Content-Language] => en-us
)

Actual result:
--------------
Array
(
    [From] => "xyz" <xyz@xyz.com>
    [To] => <xyz@xyz.com>
    [Subject] => Reply Is? white side-LED
)