[Cashtab] Patch bug caused by wallet change from Tokens page

Summary:
The screen defines tokens as wallet.state.tokens in one place, uses this value to do the calculations, but then triggers the useEffect on wallet.state.tokens.

Make sure the tokens used in the useEffect is the same tokens used in the dependency array.

Test Plan: npm test, npm start, navigate to tokens page, change wallets a few times, no white screen app crash

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16078