PCX: Fix reading of the extended palette
The VGA palette starts 769 bytes before the end of the file. There may be PADs between the end of the image and the start of the palette. BUG: 463951
The VGA palette starts 769 bytes before the end of the file. There may be PADs between the end of the image and the start of the palette. BUG: 463951
mentioned in commit bb66367b