3006 VERIFY[S,U,P] and ASSERT[S,U,P] frequently check if first argument is zero

*** 160,170 ****
          if (tbl->zt_nextblk != 0) {
                  newblk = tbl->zt_nextblk;
          } else {
                  newblk = zap_allocate_blocks(zap, tbl->zt_numblks * 2);
                  tbl->zt_nextblk = newblk;
!                 ASSERT3U(tbl->zt_blks_copied, ==, 0);
                  dmu_prefetch(zap->zap_objset, zap->zap_object,
                      tbl->zt_blk << bs, tbl->zt_numblks << bs);
          }
  
          /*
--- 160,170 ----
          if (tbl->zt_nextblk != 0) {
                  newblk = tbl->zt_nextblk;
          } else {
                  newblk = zap_allocate_blocks(zap, tbl->zt_numblks * 2);
                  tbl->zt_nextblk = newblk;
!                 ASSERT0(tbl->zt_blks_copied);
                  dmu_prefetch(zap->zap_objset, zap->zap_object,
                      tbl->zt_blk << bs, tbl->zt_numblks << bs);
          }
  
          /*
*** 337,347 ****
                  dmu_buf_t *db_new;
                  int err;
  
                  ASSERT3U(zap->zap_f.zap_phys->zap_ptrtbl.zt_shift, ==,
                      ZAP_EMBEDDED_PTRTBL_SHIFT(zap));
!                 ASSERT3U(zap->zap_f.zap_phys->zap_ptrtbl.zt_blk, ==, 0);
  
                  newblk = zap_allocate_blocks(zap, 1);
                  err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
                      newblk << FZAP_BLOCK_SHIFT(zap), FTAG, &db_new,
                      DMU_READ_NO_PREFETCH);
--- 337,347 ----
                  dmu_buf_t *db_new;
                  int err;
  
                  ASSERT3U(zap->zap_f.zap_phys->zap_ptrtbl.zt_shift, ==,
                      ZAP_EMBEDDED_PTRTBL_SHIFT(zap));
!                 ASSERT0(zap->zap_f.zap_phys->zap_ptrtbl.zt_blk);
  
                  newblk = zap_allocate_blocks(zap, 1);
                  err = dmu_buf_hold(zap->zap_objset, zap->zap_object,
                      newblk << FZAP_BLOCK_SHIFT(zap), FTAG, &db_new,
                      DMU_READ_NO_PREFETCH);
*** 473,483 ****
          /*
           * lhr_pad was previously used for the next leaf in the leaf
           * chain.  There should be no chained leafs (as we have removed
           * support for them).
           */
!         ASSERT3U(l->l_phys->l_hdr.lh_pad1, ==, 0);
  
          /*
           * There should be more hash entries than there can be
           * chunks to put in the hash table
           */
--- 473,483 ----
          /*
           * lhr_pad was previously used for the next leaf in the leaf
           * chain.  There should be no chained leafs (as we have removed
           * support for them).
           */
!         ASSERT0(l->l_phys->l_hdr.lh_pad1);
  
          /*
           * There should be more hash entries than there can be
           * chunks to put in the hash table
           */
*** 656,668 ****
  
          nl = zap_create_leaf(zap, tx);
          zap_leaf_split(l, nl, zap->zap_normflags != 0);
  
          /* set sibling pointers */
!         for (i = 0; i < (1ULL<<prefix_diff); i++) {
                  err = zap_set_idx_to_blk(zap, sibling+i, nl->l_blkid, tx);
!                 ASSERT3U(err, ==, 0); /* we checked for i/o errors above */
          }
  
          if (hash & (1ULL << (64 - l->l_phys->l_hdr.lh_prefix_len))) {
                  /* we want the sibling */
                  zap_put_leaf(l);
--- 656,668 ----
  
          nl = zap_create_leaf(zap, tx);
          zap_leaf_split(l, nl, zap->zap_normflags != 0);
  
          /* set sibling pointers */
!         for (i = 0; i < (1ULL << prefix_diff); i++) {
                  err = zap_set_idx_to_blk(zap, sibling+i, nl->l_blkid, tx);
!                 ASSERT0(err); /* we checked for i/o errors above */
          }
  
          if (hash & (1ULL << (64 - l->l_phys->l_hdr.lh_prefix_len))) {
                  /* we want the sibling */
                  zap_put_leaf(l);