Fix #2556: Show correct total BAT balance

[kylehickinson]

Summary of Changes

This pull request fixes #2556

Submitter Checklist:

• Unit Tests are updated to cover new or changed functionality
• User-facing strings use NSLocalizableString()

Test Plan:

• Ensure environment is prod, Enable Rewards
• Import Jimmy's DB (and force-quit/relaunch)
• Ensure it shows 33 BAT balance
• (Reset Rewards/delete app after so you don't spend his BAT 😜)

Reviewer Checklist:

• Issues include necessary QA labels:
  • QA/(Yes|No)
  • release-notes/(include|exclude)
  • bug / enhancement
• Necessary security reviews have taken place.
• Adequate unit test coverage exists to prevent regressions.
• Adequate test plan exists for QA to validate (if applicable).
• Issue is assigned to a milestone (should happen at merge time).

[kylehickinson]

Please do not delete branch after merge (will end up being the v1.16.2 tag)