Description:
------------
imagecreatefrompng() should not throw a fatal error
when opening broken image files. Instead, a warning would be much more useful. 

The following code is useless as the scripts dies without any output. If I remove the @, it throws the following message: 
---
Fatal error: imagecreatefrompng() [function.imagecreatefrompng]: gd-png: fatal libpng error: Invalid chunk length. in F:\htdocs\bug\read.php on line 3
---

imagecreatefrompng throws a warning when opening files that are no png files ('broken.png' is not a valid PNG file) but not when the image file is a png image, bug is broken for whatever reason. 


---
OS: Windows XP Professional
Apache: 2.0.49
PHP: 5.0.0 as apache module
GD: bundled (2.0.23 compatible)
PNG Support: enabled


Reproduce code:
---------------
<?php
$filename = 'broken.png';
$imageResource = @imagecreatefrompng($filename);
if (!$imageResource) {
	die('could not read ' . $filename . ' image');	
}
else {
	echo 'image ' . $filename . ' successfully read';	
}
?>

Expected result:
----------------
could not read broken.png image

Actual result:
--------------
Fatal error: imagecreatefrompng() [function.imagecreatefrompng]: gd-png: fatal libpng error: Invalid chunk length. in F:\htdocs\bug\read.php on line 3