message: fix(GUI): don't display hyphen in drive selection entry if no size
  Some drives, like usbboot USB devices, don't have a size associated with
  them, which results in the drive selection widget showing a hyphen with
  nothing at the side, which looks a bit weird.
diff: width="25"
  height="30">
  <div class="list-group-item-section list-group-item-section-expanded">
  - <h4 class="list-group-item-heading">{{ drive.description }} -
  - <span class="word-keep">{{ drive.size | closestUnit }}</span>
  + <h4 class="list-group-item-heading">
  + {{ drive.description }} <span class="word-keep"
  + ng-show="drive.size">- {{ drive.size | closestUnit }}</span>
  </h4>
  <p class="list-group-item-text">{{ drive.displayName }}</p>
  