Handle "Score is not between 0 and 1" canvas error, in PostGrade view

[nikolas]

The response can look like this:

'<?xml version="1.0" encoding="UTF-8"?>\n<imsx_POXEnvelopeResponse xmlns="http://www.imsglobal.org/services/ltiv1p1/xsd/imsoms_v1p0">\n        <imsx_POXHeader>\n          <imsx_POXResponseHeaderInfo>\n            <imsx_version>V1.0</imsx_version>\n            <imsx_messageIdentifier/>\n            <imsx_statusInfo>\n              <imsx_codeMajor>failure</imsx_codeMajor>\n              <imsx_severity>status</imsx_severity>\n              <imsx_description>Score is not between 0 and 1\n[EID_13960006980949683]</imsx_description>\n              <imsx_messageRefIdentifier>1512060794</imsx_messageRefIdentifier>\n              <imsx_operationRefIdentifier>replaceResult</imsx_operationRefIdentifier>\n            </imsx_statusInfo>\n          </imsx_POXResponseHeaderInfo>\n        </imsx_POXHeader>\n        <imsx_POXBody><replaceResultResponse/></imsx_POXBody>\n      </imsx_POXEnvelopeResponse>\n'

and our library just returns "Post grade failed". Give more detail here

[nikolas]

This might actually need to be addressed in PyLTI, not django-lti-provider.

I've seen other auth-related errors too that I'm only seeing because i have pylti debugging on.