fix: report filename if template file is invalid A file name like .#issue.search.html causes a crash because _find returns None not a tuple and unpacking fails. Trap the TypeError and raise ValueError with message that includes the basename of the file.

License
=======

Roundup is Free Software under the following license (from the file
COPYING.txt in the software distribution):

.. raw:: html

   <div class="file_insert">

.. include:: ../COPYING.txt

.. raw:: html

   </div>