fs/ext2: Fix out-of-bounds read for inline extents

fs/ext2: Fix out-of-bounds read for inline extents

When inline extents are used, i.e. the extent tree depth equals zero,
a maximum of four entries can fit into the inode's data block. If the
extent header states a number of entries greater than four the current
ext2 implementation causes an out-of-bounds read. Fix this issue by
capping the number of extents to four when reading inline extents.

Reported-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Chang <mchang@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>