[pdq] ValueError when computing PDQ hash on some pngs

[thedanielsun]

Getting a rare, sporadic error when computing PDQ hash for certain images

Repro below:

$ threatexchange hash photo https://styles.redditmedia.com/t5_6k8ysb/styles/profileIcon_jj0se5l3qgrd1.png
Traceback (most recent call last):
  File "/Users/daniel.sun/.pyenv/versions/3.8.12/bin/threatexchange", line 8, in <module>
    sys.exit(main())
  File "/Users/daniel.sun/.pyenv/versions/3.8.12/lib/python3.8/site-packages/threatexchange/cli/main.py", line 333, in main
    inner_main()
  File "/Users/daniel.sun/.pyenv/versions/3.8.12/lib/python3.8/site-packages/threatexchange/cli/main.py", line 326, in inner_main
    execute_command(settings, namespace)
  File "/Users/daniel.sun/.pyenv/versions/3.8.12/lib/python3.8/site-packages/threatexchange/cli/main.py", line 161, in execute_command
    command.execute(settings)
  File "/Users/daniel.sun/.pyenv/versions/3.8.12/lib/python3.8/site-packages/threatexchange/cli/hash_cmd.py", line 106, in execute
    hash_str = hasher.hash_from_file(file)
  File "/Users/daniel.sun/.pyenv/versions/3.8.12/lib/python3.8/site-packages/threatexchange/signal_type/signal_base.py", line 196, in hash_from_file
    return cls.hash_from_bytes(file.read_bytes())
  File "/Users/daniel.sun/.pyenv/versions/3.8.12/lib/python3.8/site-packages/threatexchange/signal_type/pdq/signal.py", line 79, in hash_from_bytes
    pdq_hash, quality = pdq_from_bytes(bytes_)
  File "/Users/daniel.sun/.pyenv/versions/3.8.12/lib/python3.8/site-packages/threatexchange/signal_type/pdq/pdq_hasher.py", line 32, in pdq_from_bytes
    return _pdq_from_numpy_array(np_array)
  File "/Users/daniel.sun/.pyenv/versions/3.8.12/lib/python3.8/site-packages/threatexchange/signal_type/pdq/pdq_hasher.py", line 36, in _pdq_from_numpy_array
    hash_vector, quality = pdqhash.compute(array)
  File "pdqhash/bindings.pyx", line 66, in pdqhash.bindings.compute
ValueError: Buffer dtype mismatch, expected 'char' but got 'int'

Verified this occurs on threatexchange version 1.1.1 (but on python 3.8)

[Dcallies]

Thanks a ton for the bug report @thedanielsun! A bit overwhelmed after the hackathon, but I'll aim to get a repro and then some debugging. If you end up needed it fixed faster and solve it on your own, feel free to submit the fix as a comment or PR!