Fixed a few things that the fuzz tester found (#122)
Fixed a few things that the fuzz tester found (#122)

* Fixed a few things that the fuzz tester found
* png palette must be from 1 - 256 inclusive
* Indexed PNG must have a palette
* BMP width cannot be -(2 << 31)
* Remove some unsigned overflow warnings (just to avoid the warning - no actual bug here)
AndreRenaud/PDFGen,AndreRenaud/PDFGen,AndreRenaud/PDFGen