Properly handle decimal point in ETH inputs

[rdig]

Description

This issue arose as just entering a decimal point (no other values), into a ETH input, would then send that value (just the . string) to the EthUsd component which attempted to convert it to USD, which would obviously fail.

Here is a demo of setting a task payout, before making this change:

There are just two places we use a token / ETH input:

• moving tokens between domain pots
• setting task's payout

Changes

• TokensMoveDialogForm skip ETH conversion if amount is just .
• TaskEditDialog skip ETH conversion if payout amount is just .

Demo

Resolves #2009

[ceolson01]

This is a fine solution - as a user, it's what I'd expect to happen when entering .. Also, this mimics the behavior of other financial applications I use.

Nice work, LGTM ✅