Elements-qt mixes asset values when clicking "Use Available balance"

[andreabonel]

When we try to send different assets in the same transaction and we click on Use available balance the "Amount" is miscalculated by mixing different assets.

Example:

My wallet currently has 0.00228895 L-BTC.

I try to send 0.0022 of asset 160d16ed964e65405d654427f141349847b238cbba34ccd78e09cd47e5dd0a94.

Then I click on Add Recipient to try to send some L-BTC.
When clicking on Use available balance I'd expect "Amount" to show 0.00228895 L-BTC but I get 0.00008895 instead.

I'm using Elements v22.1.0rc1.