Description:
------------
I'm trying to add zeros before string if the length of string is lower than, let's say 8.

Function is not checking the given string length, if the length is same than it should return, sprintf() will replace ALL chars with zero (see examples).

Reproduce code:
---------------
$hex = 'F5F2F4';
return sprintf("%08d", $hex);

=> Returns 000F5F2F4 like it should be

$hex = 'F2F45F2F4';
return sprintf("%08d", $hex);

=> Returns 00000000, not F2F45F2F4 like it should be

Expected result:
----------------
$hex = 'F5F2F4';
return sprintf("%08d", $hex);

=> Returns 000F5F2F4 like it should be

$hex = 'F2F45F2F4';
return sprintf("%08d", $hex);

=> Returns 00000000, not F2F45F2F4 like it should be

Actual result:
--------------
$hex = 'F5F2F4';
return sprintf("%08d", $hex);

=> Returns 000F5F2F4 like it should be

$hex = 'F2F45F2F4';
return sprintf("%08d", $hex);

=> Returns 00000000, not F2F45F2F4 like it should be