serve: Don't crash when a post URL doesn't match our expectations. It can happen that a posts source's URL pattern matches that of something else, like a taxonomy page. In this case, don't crash when what we think will be integers turn out to be something else. Instead, just return that no page has been found.

[pytest]
norecursedirs = .* _darcs CVS .svn .git .hg *.egg-info dist build node_modules venv tmp* {args}