Missing raise for non-400 errors when creating an image

This except clause is missing a raise when the error is not a HTTP 400, causing this error:

[INFO] Creating image for page 10470771
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/local/lib/python3.7/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/local/lib/python3.7/site-packages/arkindex_tasks/import_transkribus.py", line 437, in <module>
    main()
  File "/usr/local/lib/python3.7/site-packages/arkindex_tasks/import_transkribus.py", line 433, in main
    TranskribusImporter(**args).run()
  File "/usr/local/lib/python3.7/site-packages/arkindex_tasks/import_transkribus.py", line 367, in run
    line_type=self.line_type,
  File "/usr/local/lib/python3.7/site-packages/arkindex_tasks/import_transkribus.py", line 243, in run
    line_type=self.line_type,
  File "/usr/local/lib/python3.7/site-packages/arkindex_tasks/import_transkribus.py", line 169, in run
    self.upload_image()
  File "/usr/local/lib/python3.7/site-packages/arkindex_tasks/import_transkribus.py", line 71, in upload_image
    logger.info("Validating image {}".format(self.image["id"]))
AttributeError: 'TranskribusElement' object has no attribute 'image'