Avoid overflow when reading corrupt cpio archive

Avoid overflow when reading corrupt cpio archive

A cpio "newc" archive with a namelength of "FFFFFFFF", if read on a
system with a 32-bit size_t, would result in namelength + name_pad
overflowing 32 bits and libarchive attempting to copy 2^32-1 bytes
from a 2-byte buffer, with appropriately hilarious results.

Check for this overflow and fail; there's no legitimate reason for a
cpio archive to contain a file with a name over 4 billion characters
in length.

Reported by:	Eyal Itkin
Security:	Corrupt archives can cause libarchive to crash on
		32-bit platforms.
Sponsored by:	Tarsnap Backup Inc.