zoekt-webserver: Work With Empty Index Directory

[dharesign]

I have configured two services, one running zoekt-indexserver and another zoekt-webserver. On a freshly configured system, the web server fails to start until the index server has written the first item to the index directory.

It fails here.

It would be nice if the web server could come up immediately.

[hanwen]

yeah, I added this to guard against operator error, but maybe we should just remove this check. Send a change? (see CONTRIBUTING)