Dataframe containing a Segarray .__str__() bug

[stress-tess]

attempting to print a dataframe containing a segarray results in AttributeError: 'SegArray' object has no attribute 'nbytes'

df_dict = dict()
num_rows = 10
val_size = num_rows
first_last_empty_vals = ak.randint(-2**10, 2**10, val_size)
first_last_empty_segs = ak.concatenate([ak.array([0,0,0]), ak.sort(ak.randint(0, val_size, num_rows-6)), ak.array([val_size, val_size, val_size])])
sa = ak.SegArray(first_last_empty_segs, first_last_empty_vals)
df_dict['all_in_first'] = sa

# this works
print(ak.DataFrame(df_dict).__repr__())

# this doesn't
print(ak.DataFrame(df_dict).__str__())