0 Money payment in invoice and bill

[batuhawk]

Steps to reproduce the issue

If i create new invoice or bill and after i want to pay for both of them with 0 money it doesn't matter what use my currency type its happening but it shouldn't be.

Expected result

Not pay with 0 money

Actual result

We can add 0 money.

System information (Akaunting, PHP versions)

Akaunting : 1.2.12
Php version : 7.1