Floss: Refresh peripheral battery data if cache is empty

The Bluetooth stack restarts when a user signs out, so cached battery
data is cleared. This change manually refreshes peripheral battery data
if the battery data cache is empty.

Bug: 331896555
Test: m && manually with Logitech Casa Keys, signing out and in
Flag: EXEMPT, Floss only
Change-Id: I758f6d90a7c8047d69ae9f808ea378ac7588af5a