Handle case where template file doesn't exist. If a template file is a dangling symbolic link, it used to raise a "TypeError: 'NoneType' object is not iterable". Replace that useless error with a NoTemplate exception reporting the problem file.

[run]

# ignore the dist utils. They are not part of the code base
# we are going to test. They are used by maintainers only.
omit = roundup/dist/*