Indexed png transparency increased to incorrrect length of 255

[jamesbrobb]

Hi,

in png.js at line 135 you're incorrectly lengthening transparency.indexed to 255, if it's shorter.

The max length of that array should actually be the length of the palette divided by 3. And if it's parsed and is any longer there should be an error.

So it should read,

short = (this.palette.length/3) - this.transparency.indexed.length;