libext2fs/e2fsck: don't run off the end of the EA block

libext2fs/e2fsck: don't run off the end of the EA block

When we're (a) reading EAs into a buffer; (b) byte-swapping EA
entries; or (c) checking EA data, be careful not to run off the end of
the memory buffer, because this causes invalid memory accesses and
e2fsck crashes.  This can happen if we encounter a specially crafted
FS image.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>