Print method bugs when a table only has taxon ID

[zachary-foster]

> result
<Taxmap>
  17 taxa: b. Mammalia, c. Plantae, d. Felidae, e. Notoryctidae ... p. sapiens, q. lycopersicum, r. tuberosum
  17 edges: NA->b, NA->c, b->d, b->e, b->f, c->g, d->h, d->i, e->j, f->k, g->l, h->m, i->n, j->o, k->p, l->q, l->r
  4 data sets:
    info:
      # A tibble: 6 x 1
        taxon_id
        <chr>   
NANANA
NANANA
NANANA
      # ... with 3 more rows
    phylopic_ids: a named vector of 'character' with 6 items
       m. e148eabb-f138-43c6-b1e4-5cda2180485a ... r. 63604565-0406-460b-8cb8-1abe954b3f3a
    foods: a list of 6 items named by taxa:
       m, n, o, p, q, r
    abund:
      # A tibble: 8 x 5
        taxon_id code  sample_id count taxon_index
        <chr>    <fct> <fct>     <dbl>       <int>
      1 m        T     A            1.           1
      2 n        C     A            2.           2
      3 o        M     B            5.           3
      # ... with 5 more rows
  1 functions:
    reaction