[Cashtab] Support locale display for locales with no thousands separator

Summary:
T3507

For locales that do not have a thousand separator, this formatting function may be using '0' -- resulting in the wrong amount being displayed.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D15886