Max Button on `Lock OMN token Modal` is not working

[pimato]

Describe the bug It looks like once a user clicks on Max, the inputfield is getting empty: https://user-images.githubusercontent.com/5337809/129029630-5d0e9ec1-5ffd-4ddf-8c36-6ab94e70cc26.mov

To Reproduce Steps to reproduce the behavior:

1. Go to 'http://localhost:3000/#/liquidity'
2. Click on 'Omen Button'
3. Click on 'Lock OMN'
4. Set 5 in the Inputfield
5. Click on 'Max'
6. Result: Inputfield Empty == no value

Expected behavior Clicking on Max button should input the total available amount of OMN tokens which can be locked from the Omen Account.