3955 ztest failure: assertion refcount_count(&tx->tx_space_written) + delta <= tx->tx_space_towrite
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>

@@ -446,16 +446,16 @@
                 }
         } else {
                 blkid = off >> dn->dn_datablkshift;
                 nblks = (len + dn->dn_datablksz - 1) >> dn->dn_datablkshift;
 
-                if (blkid >= dn->dn_maxblkid) {
+                if (blkid > dn->dn_maxblkid) {
                         rw_exit(&dn->dn_struct_rwlock);
                         return;
                 }
                 if (blkid + nblks > dn->dn_maxblkid)
-                        nblks = dn->dn_maxblkid - blkid;
+                        nblks = dn->dn_maxblkid - blkid + 1;
 
         }
         l0span = nblks;    /* save for later use to calc level > 1 overhead */
         if (dn->dn_nlevels == 1) {
                 int i;