Allow starting without web config

This pull request makes a non-existant `etc/web.ini` no longer a reason for bailing before startup. It can perfectly make sense, e.g. to simply start serving static contents:

```sh
$ find . | grep -v .git
.
./README.md
./static
./static/index.html

$ xpws
# now open http://localhost:8080/index.html
```