Bug 1094878 - Call is not on hold anymore after hanging up another call even though the icon says it is

I don't really like this comment. Here is my suggestion:
```js
  // Stores the HandledCall held by the user pressing the 'Hold' button. Null
  // if: there is no call on hold, or the user the didn't hold it by pressing
  // the 'Hold' button.
```