Show "0" instead of "0 B" in storage settings.

Two benefits:
  - "0 B" might be a little confusing for sighted users
  - "zero bee" is definitely confusing for TalkBack users

Nonzero storage items will still read as "640 KB" which
should be enough for anyone.

Change-Id: I5c89f7c6382ca14fb91d7d1dd145977f855618ae
Fixes: 27973778