libext2fs: iterate past lower extents during punch

libext2fs: iterate past lower extents during punch

When we're iterating extents during a punch operation, the loop exits
if the punch region is entirely to the right of the extent we're
looking at.  This can happen if the punch region starts in the middle
of a hole and covers mapped extents.  When this happens, we want to
skip to the next extent, because it might be punchable.

Also, if we've totally passed the punch range, stop.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>