Fix ringtone pref summary stuck on "Loading ringtone..."

When the default alarm ringtone has been deleted, the alarm
pref can't resolve the ringtone URI and never finishes loading
a reasonable default string. In these cases, the Clock app
actually does play a default tone, so it's not necessary to
have the UI select a new tone, but it does need to show
something reasonable in the summary. Fix this in 3 ways:
* Do not resolve actual URI for a default URI when looking
  up the title. This brings back the "Default ringtone (xxx)"
  string that used to appear in GB on individual alarms with
  no specific ringtone selected.
* In the default alarm pref, we do still want to resolve an
  actual URI since the "Default ringtone" string would be
  redundant. But when the default has been deleted, show a
  reasonable default string by asking for the default alarm's
  title without resolving to an actual URI. This does mean
  the summary will show "Default ringtone (xxx)" when a default
  has been deleted, but it's better than nothing, and it's
  consistent with individual alarms with unresolvable ringtones.
* If even the default URI fails to resolve to a string, at least
  clear the "Loading ringtone..." string. This generally will
  not happen.

Bug: 5091775
Change-Id: I9a6f7117e1b4c3c36aed59a4e4e527d955f02361