Make inputlist behave more like description

The default (non-changeable) description shown at the bottom of an
iputlist is

  Type number and <Enter> or click with mouse (empty cancels):

Due to how our inputlist was setup, empty didn't cancel - it selected
the first file. I read up on the vim docs, and found this:

  It's a good idea to put the entry number at the start of the string.
  And put a prompt in the first item.
  Example:
    let color = inputlist(['Select color:', '1. red',
           \ '2. green', '3. blue'])

From http://vimdoc.sourceforge.net/htmldoc/eval.html#inputlist()