Description:
------------
The functions getimagesize, and getimagesizefromstring treat the height field of a BITMAPINFOHEADER header as an unsigned integer, while it really is a signed integer. On platforms with 64 bit PHP integers, this results in height being reported as 4294966272 for an image with height -1024, instead of the expected result height=1024.

Test script:
---------------
<?php
$image_data = "Qk06AAAAAAAAADYAAAAoAAAAAQAAAP////8BABgAAAAAAAQAAADDDgAAww4AAAAAAAAAAAAA////AA==";
var_dump(getimagesizefromstring(base64_decode($image_data)));
?>

Expected result:
----------------
array(6) {
  [0]=>
  int(1)
  [1]=>
  int(1)
  [2]=>
  int(6)
  [3]=>
  string(20) "width="1" height="1""
  ["bits"]=>
  int(24)
  ["mime"]=>
  string(14) "image/x-ms-bmp"
}

Actual result:
--------------
array(6) {
  [0]=>
  int(1)
  [1]=>
  int(4294967295)
  [2]=>
  int(6)
  [3]=>
  string(21) "width="1" height="-1""
  ["bits"]=>
  int(24)
  ["mime"]=>
  string(14) "image/x-ms-bmp"
}