parse_string_from_args: UnicodeDecodeError: 'ascii' codec can't decode byte: ordinal not in range(128)

[erikjohnston]

https://sentry.matrix.org/new-vector/synapse-matrixorg/issues/20/

UnicodeDecodeError: 'ascii' codec can't decode byte 0xe2 in position 23: ordinal not in range(128)
  File "/home/matrix/synapse/synapse/http/server.py", line 81, in wrapped_request_handler
  File "/home/matrix/.synapse-py36/lib/python3.6/site-packages/twisted/internet/defer.py", line 1418, in _inlineCallbacks
  File "/home/matrix/synapse/synapse/rest/media/v1/preview_url_resource.py", line 110, in _async_render_GET
  File "/home/matrix/synapse/synapse/http/servlet.py", line 144, in parse_string
  File "/home/matrix/synapse/synapse/http/servlet.py", line 158, in parse_string_from_args

Failed handle request via u'PreviewUrlResource': u"<XForwardedForRequest at 0x7f77a7542ba8 method='GET' uri='/_matrix/media/r0/preview_url?url=<redacted>&ts=1551862120266' clientproto='HTTP/1.1' site=8085>"

[erikjohnston]

Duplicate of #4585