Clicking "max" btn for a reverse swap was setting the text field to a too high value.
```
>>> wallet.lnworker.num_sats_can_send()
Decimal('1242647.947')
>>> util.format_satoshis_plain(Decimal('1242647.947'))
'0.01242648'
```
Clicking "max" btn for a reverse swap was setting the text field to a too high value.
```
>>> wallet.lnworker.num_sats_can_send()
Decimal('1242647.947')
>>> util.format_satoshis_plain(Decimal('1242647.947'))
'0.01242648'
```