Comment 1 for bug 353805

Reproducer (works on staging):

b=lp.bugs[89040]
b.addAttachment(comment='', data=open('thread.txt').read(), description='test353805', filename='test353805', is_patch=False)

This apparently happens because something in launchpadlib assumes that data is UTF-8 encoded. While stack traces are by and large text, they can have binary stuff in it, such as this one.