TokenProcessor - If there is a `locale`, then use it

TokenProcessor - If there is a `locale`, then use it

There are two likely ways in which a tokenized email winds up with localized strings - either
the Smarty `{ts}...{/ts}` tags define it, or a custom/hook-based tag uses `ts()`.

This ensures that the locale is set in both cases.

It's hypothetically possible that some other `civi.token.eval` listeners
need to use the `row->context['locale']`.  However, I grepped universe and
couldn't find anything that would be affected.  (There were two contrib
listeners for `civi.token.eval` and neither seemed to be affected.)