ext2fs: Fix old out-of-bounds access.

Overrunning buffer pointed to by (caddr_t)&oip->i_db[0] of 48 bytes by
passing it to a function which accesses it at byte offset 59 using
argument 60UL.

The issue was inherited from an older FFS implementation and
fixed there with by merging UFS2 in r98542. We follow the
FFS fix.

Discussed with:	bde
CID:		1007665
MFC after:	3 days