WebUI should allow you to open a channel without any balance

[LefterisJP]

I tried to open a channel without any balance and the webui does not let me. This should just work. Any idea why it is currently not allowed?

[kelsos]

@LefterisJP there is a validation requiring the channel balance to be more than zero, I don't remember if that was there before or if I inserted it due to erroneous assumptions but it should be an easy fix though.