sceIoDread() should return 1 when there are more.

Before it was returning > 1 if there were many more, which the PSP
did not do.
Correctly read ISO 9660 directory entries.

Before, we would often duplicate the last entry in a directory.
Merge pull request #635 from unknownbrackets/io-minor

Fix sceIoDread() and ISO 9660 directory reading