misc: fix 'zero_hugefiles = false' regression

misc: fix 'zero_hugefiles = false' regression

When mk_hugefiles() was switched to use ext2fs_fallocate(), it was
accidentally changed to ignore the 'zero_hugefiles = false' setting,
which should cause hugefiles to be allocated without initializing their
contents.  Fix this by only passing EXT2_FALLOCATE_ZERO_BLOCKS to
ext2fs_fallocate() when zero_hugefiles is true.

Google-Bug-Id: 38037607
Fixes: 4f868703f6f2 ("libext2fs: use fallocate for creating journals and hugefiles")
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>