Default error code to 500

[fixes #18]

{{cookiecutter.app_name}}/{{cookiecutter.app_name}}/app.py

@@ -48,7 +48,9 @@ def register_blueprints(app):
 
 def register_errorhandlers(app):
     def render_error(error):
-        return render_template("{0}.html".format(error.code)), error.code
+        # If a HTTPException, pull the `code` attribute; default to 500
+        error_code = getattr(error, 'code', 500)
+        return render_template("{0}.html".format(error_code)), error_code
     for errcode in [401, 404, 500]:
         app.errorhandler(errcode)(render_error)
     return None