There is some code that tries to update the amounts in the widgets of the send and receive tab when the unit is changed in the preferences menu.
But there were two issues:
- the `decimal_point` attribute was not updated in `XECAmountEdit`
- the base unit string was not updated in `SettingsDialog` and there was some code preventing the `unit_changed` signal from being emitted if the base_unit attribute was equal to the newly selected unit, so the signal was not emitted when changing to a new unit then back to the previous unit
After fixing the `self.base_unit` update in SettingsDialog, the `if self.base_unit == unit_result:` branch becomes dead code because the `on_unit` method is only called when the unit actually changes. So we can just remove that `self.base_unit` attribute which is not used anywhere else.