Don't set the "incomplete" bit for empty numbers.

There will never be contact information for an empty number, so don't bother trying to look them up at render time.

This also prevents a crash in the new voicemail fragment that occurs due to an assertion that voicemail rows will never be incomplete, when it may be possible for a voicemail to exist with an empty number.

Also, don't set short numbers in VoicemailPopulator, since we don't expect this to be possible and would like to avoid crashing in the aforementioned assertion when using simulator.

Test: unit
PiperOrigin-RevId: 184615402
Change-Id: I5286112b57179e002f04de81c04475f30b3e1833