ceph: fix ENOENT logic in striped_read

Getting ENOENT is equivalent to reading 0 bytes.  Make that correction
before setting up the hit_stripe and was_short flags.

Fixes the following case:
 dd if=/dev/zero of=/mnt/fs_depot/dd3 bs=1 seek=1048576 count=0
 dd if=/mnt/fs_depot/dd3 of=/root/ddout1 skip=8 bs=500 count=2 iflag=direct

Reported-by: Henry C Chang <henry.cy.chang@gmail.com>
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/file.c

@@ -318,10 +318,10 @@ more:
 				  ci->i_truncate_seq,
 				  ci->i_truncate_size,
 				  page_pos, pages_left, page_align);
-	hit_stripe = this_len < left;
-	was_short = ret >= 0 && ret < this_len;
 	if (ret == -ENOENT)
 		ret = 0;
+	hit_stripe = this_len < left;
+	was_short = ret >= 0 && ret < this_len;
 	dout("striped_read %llu~%u (read %u) got %d%s%s\n", pos, left, read,
 	     ret, hit_stripe ? " HITSTRIPE" : "", was_short ? " SHORT" : "");