Parsing of profile img may fail for corner-cases when running experimental / next

[jonasbardino]

The crash ends up something like:

TypeError: a bytes-like object is required, not 'str'
Traceback (most recent call last):
  File "/home/mig/mig/wsgi-bin/migwsgi.py", line 124, in stub
    (output_objects, (ret_code, ret_msg)) = main(client_id,
  File "/home/mig/mig/shared/functionality/viewuser.py", line 244, in main
    user_item = build_useritem_object_from_user_dict(configuration,
  File "/home/mig/mig/shared/functionality/viewuser.py", line 113, in build_useritem_object_from_user_dict
    img_data = inline_image(configuration, img_path)
  File "/home/mig/mig/shared/user.py", line 151, in inline_image
    img_data = ''
  File "/usr/lib64/python3.9/base64.py", line 58, in b64encode
    encoded = binascii.b2a_base64(s, newline=False)

when a bogus empty string is found and we try to do byte vs str conversion assuming a non-empty string.