e2fsck: Add check to enforce a valid block bitmap in last block group

e2fsck: Add check to enforce a valid block bitmap in last block group

Add a check for the UNINIT_BLOCKS flag set in the last group.  The kernel
patch doesn't handle this gracefully, because it assumes there are a full
set of blocks in each group marked UNINIT_BLOCKS.  The kernel should be
fixed up, but in the meantime this avoids hitting the problem, and is
more consistent with lazy_bg not marking the last group UNINIT.

Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>