Description:
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Getimagesize still gives errors for .ico files or no information at all. Also, there is no predefined constant for this type of image files.
Considering that .ico is older than .png I believe that .ico should have full support.

Reproduce code:
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$tmp='/tmp/favicon.ico';
$buffer=file_get_contents('http://www.favicon.com/favicon.ico');
file_put_contents($tmp,$buffer);
list($ox, $oy, $type, $attr) = getimagesize($tmp);
echo "ox={$ox}<br>oy={$oy}<br>type={$type}<br>attr={$attr}<br>size=".filesize($tmp)."<br>";


Expected result:
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ox=16
oy=16
type=???
attr=
size=318

Actual result:
--------------
ox=
oy=
type=
attr=
size=318

getimagesize actually does not return any information at all about this image file.