Assume first directory if only one is configured

[wincent]

Via an email:

... for the first time in a new session, I get :Corpus autocompleted in the cmd window, but corpus is not showing a list of notes. I then either have to TAB to get it to autocomplete the dir mentioned in CorpusDirectories or simply press enter. Both cases does not do anything and I have to do the shortcut again to start corpus list/preview.

I can imagine this is for setting the "current" corpusDirectory you want to preview / work with - that's nice. But if I only have one directory, I think Corpus should be "intelligent" enough to select the first one and display the list right away.