BUG: HSA raise the correct error rather than LoginError

I am trying to search the herschel archive for multiple sources (I'll wait to hit it with 1000's, but am testing now with 10). I am seeing a strange "LoginError: Data protected by proprietary rights. Please check your credentials".
1. I can't imagine that there is herschel proprietary data still, given that the telescope hasn't taken data in years, so I am guessing something else is going on, but have sent a herschel helpdesk message to see if I can't get a definitive answer on that.
2. I tried a "try except" around the call to say don't grab those observation_id that appear to be proprietary, but python won't let me do an
` except LoginError`. It tells me "NameError: name 'LoginError' is not defined". (and I tried, but it doesn't work to 'except NameError')

Is it possible for astroquery to throw some other, recognizable error, so I can move around this problem? I'll take other suggested workarounds!

Thanks,

minimum example, using the coords and syntax for query_hsa_tap that are listed in the astroquery readthedocs page (https://astroquery.readthedocs.io/en/latest/esa/hsa/hsa.html):

```
from astroquery.esa.hsa import HSA

test_table = HSA.query_hsa_tap("select top 10 observation_id from hsa.v_active_observation where "
"contains(point('ICRS', hsa.v_active_observation.ra, hsa.v_active_observation.dec), "
"circle('ICRS', 100.2417,9.895, 1.1))=1")

for row in test_table:
print(str(row['observation_id']) ) #confirm that syntax is not the problem
try:
HSA.download_data(observation_id=str(row['observation_id']), retrieval_type='OBSERVATION',
instrument_name='PACS', download_dir = 'data/herschel')
except LoginError:
#there is some problem here with the observation_id which causes Herschel to think it is proprietary
#we just won't get this data, move on to the next observation
print("loginerror")
```

Start with the HSA.query_hsa_tap and HSA.download_data entry points and reproduce the minimum example against the Herschel archive. Trace how the proprietary-data response becomes LoginError and identify a recognizable exception callers can catch. Done means the failure raises the intended exception for affected observations without changing successful downloads.

Written by the indexing model from the issue text.