Correct return values, validation in sdkver funcs

I am unable to reproduce any validation, so these changes make it match tests on a PSP.  But then, maybe it's my custom firmware getting in the way?  Added reporting to see the effect better.

I'm pretty sure we've seen games that said the version was invalid.  This may improve those games, not sure.  It may also improve any game that expects a return value of 0.

See also hrydgard/pspautotests#132.

-[Unknown]