Move checking for invalid zero blocks and setting of various iomap flags
into this helper.  Also make it deal with "raw" delalloc extents to
avoid clutter in the callers.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>