courseware/views.py index function unicode error correction and test

@adampalay @sarina 

https://edx-wiki.atlassian.net/browse/LMS-2488

The unicode input now correctly results in a 404 error instead of a 500 error.
check out our style guide for breaking long lines: https://github.com/edx/edx-platform/wiki/Python-Guidelines#breaking-long-lines