Description:
------------
pdf_open_image_file() crashes Apache while attempting to load TiFF file.

Reproduce code:
---------------
<?php

$pdf = pdf_new();
pdf_open_file($pdf);
pdf_begin_page($pdf, 200, 200);

//this function crashes
$pdfimage = pdf_open_image_file($pdf, "tiff", "test.tif");
//pdf_place_image($pdf, $pdfimage, 10, 10, 0.6);
//pdf_close_image($pdf, $pdfimage);

//close it up
pdf_end_page($pdf);
pdf_close($pdf);
$data = pdf_get_buffer($pdf);

?>


Actual result:
--------------
Start of function trace
    0.0021          0     -> pdf_new() C:\MyFiles.XFiles\Numerald\test18.php:5
    0.0025          0     -> pdf_open_file(resource(2) of type (pdf object)) C:\wwwroot\test18.php:6
    0.0029          0     -> pdf_begin_page(resource(2) of type (pdf object), 200, 200) C:\wwwroot\Numerald\test18.php:11
    0.0040          0     -> pdf_open_image_file(resource(2) of type (pdf object), 'tiff', 'test.tif') C:\wwwroot\Numerald\test18.php:14