Use available balance switches in elements-qt to Bitcoin even if a different asset is selected

Have a wallet that has multiple assets.

Select a non-bitcoin asset on the Send tab. click "use available balance". The amount used is the Bitcoin amount, not the asset.

Reproduce the issue in elements-qt with a wallet containing multiple assets: select a non-Bitcoin asset on the Send tab and click “use available balance.” Trace the Send-tab action that supplies the amount; done means it uses the selected asset’s available balance rather than Bitcoin’s amount.

Written by the indexing model from the issue text.