libext2fs: clamp block-map punch range end to 2^32 blocks

libext2fs: clamp block-map punch range end to 2^32 blocks

In the ^extent case, passing ~0ULL as the 'end' parameter to
ext2fs_punch() causes the (end - start + 1) calculation to overflow to
zero.  Since the old-style mapped block files cannot have more than
2^32 blocks, just clamp it to ~0U.

This fixes a regression in t_quota_2off with the patch "libext2fs: use
ext2fs_punch() to truncate quota file" applied.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>