resize2fs: Move all required blocks for ext4 filesystems

resize2fs: Move all required blocks for ext4 filesystems

In the function blocks_to_move(), when checking to see if a block
group's block bitmap is initialized, we need to check the old_fs's
block group descriptors, not the new file system's (already truncated)
group descriptor data structures.  Otherwise we will end up
derferencing past the end of the array boundary, and the resulting
garbage value may indicate that the bitmap is uninitialized, and so
all of the blocks in that block group will be skipped, resulting in
some blocks not getting marked as needing relocation.

This showed up in the following test case:

     mke2fs -t ext4 -b 1024 test.img 1048576
     resize2fs test.img 80000

The journal inode after the resize operation looked like this:

debugfs:  stat <8>
Inode: 8   Type: regular    Mode:  0600   Flags: 0x80000
...
BLOCKS:
(IND):35385, (0-5836):2356-8192, (5837-21959):8454-24576, (21960-32506):24838-35
384, (32507-32767):434177-434437
TOTAL: 32769

The blocks 434177-434437 were not moved because block group 53 was
wrongly thought to have an unitialized block group.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>