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

*** 504,514 ****
                              obj, zap->zap_m.zap_num_entries);
                          *zapp = zap;
                          return (mzap_upgrade(zapp, tx, 0));
                  }
                  err = dmu_object_set_blocksize(os, obj, newsz, 0, tx);
!                 ASSERT3U(err, ==, 0);
                  zap->zap_m.zap_num_chunks =
                      db->db_size / MZAP_ENT_LEN - 1;
          }
  
          *zapp = zap;
--- 504,514 ----
                              obj, zap->zap_m.zap_num_entries);
                          *zapp = zap;
                          return (mzap_upgrade(zapp, tx, 0));
                  }
                  err = dmu_object_set_blocksize(os, obj, newsz, 0, tx);
!                 ASSERT0(err);
                  zap->zap_m.zap_num_chunks =
                      db->db_size / MZAP_ENT_LEN - 1;
          }
  
          *zapp = zap;
*** 599,609 ****
          if (flags != 0) {
                  zap_t *zap;
                  /* Only fat zap supports flags; upgrade immediately. */
                  VERIFY(0 == zap_lockdir(os, obj, tx, RW_WRITER,
                      B_FALSE, B_FALSE, &zap));
!                 VERIFY3U(0, ==, mzap_upgrade(&zap, tx, flags));
                  zap_unlockdir(zap);
          }
  }
  
  int
--- 599,609 ----
          if (flags != 0) {
                  zap_t *zap;
                  /* Only fat zap supports flags; upgrade immediately. */
                  VERIFY(0 == zap_lockdir(os, obj, tx, RW_WRITER,
                      B_FALSE, B_FALSE, &zap));
!                 VERIFY0(mzap_upgrade(&zap, tx, flags));
                  zap_unlockdir(zap);
          }
  }
  
  int