The only path to `handleFirstIncomingCall()` is to `addCall` a call (with an _incoming_ state) to a previously empty `handledCalls` array.
And the only place we call `addCall` is in the `telephony.calls.forEach` in `onCallsChanged()`.

So we _definitely_ ( ;) ) go through `onCallsChanged` with `telephony.calls.length > 0` before hitting `handleFirstIncomingCall`.