Description:
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Using getimagesize on a .ico file that is 256px wide or 256px high will result in that value being returned at 0 due to the value being stored as 0 in the header as per https://devblogs.microsoft.com/oldnewthing/20101022-00/?p=12473 and https://en.wikipedia.org/wiki/ICO_(file_format):

> The value 0 is accepted as representing a width or height of 256.

> Can be any number between 0 and 255. Value 0 means 256 pixels.

Wasn't sure what version to pick as the bug is like 14 years old (introduced via https://github.com/php/php-src/commit/c76e8e03a1cc67d695b1fa024924a462ca897434), so I just with with irrelevant as it's been an issue since 5.3.0.

Test script:
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var_dump(getimagesize("https://raw.githubusercontent.com/toy/image_size/master/spec/images/ico/32x256.ico"));

Expected result:
----------------
array(6) {
  [0]=> int(32)
  [1]=> int(256)
  [2]=> int(17)
  [3]=> string(21) "width="32" height="256""
  ["bits"]=> int(8)
  ["mime"]=> string(24) "image/vnd.microsoft.icon"
}

Actual result:
--------------
array(6) {
  [0]=> int(32)
  [1]=> int(0)
  [2]=> int(17)
  [3]=> string(21) "width="32" height="0""
  ["bits"]=> int(8)
  ["mime"]=> string(24) "image/vnd.microsoft.icon"
}