C (clear) button doesn't clear the input in exchange/unit tab

[metzger100]

Current behaviour: Clear does replace the input with zero. When entering new numbers it adds them behind that zero.

Expected behaviour: Clear does remove the input. When entering new numbers it show the number.

Steps to reproduce:

1. Enter a number (100 in this example) into a currency/unit field
2. press clear
3. enter a number into the currency/unit field
4. Result: Input field: 0100