libext2fs: Add sanity checks to ext2fs_{block,inode}_alloc_stats

libext2fs: Add sanity checks to ext2fs_{block,inode}_alloc_stats

If ext2fs_inode_alloc_stats2() or ext2fs_block_alloc_stats() is passed
an insanely large inode or block number, it's possible for these
functions to overrun an array boundary and cause the calling program
to crash with a memory error.

Detect this case, and since these functions don't return an error
code, print a warning message, much like we do in ext2fs_warn_bitmap2().

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