Fix/nan income sources if income is empty

[alexanderameye]

When totalIncome is 0, then the percentages show up as NaN. This sets the percentages to 0 if they could not be calculated.

before

after

Could alternatively do something like this, I see this happens in other places in the code base.

[alexanderameye]

Put changes in https://github.com/afadil/wealthfolio/pull/58