Parsing "-" as integer incorrectly gives Ok(0)

[krdln]

Assertion in the following code is accepted, which breaks the behaviour I was relying on.

fn main() {
    assert_eq!("-".parse(), Ok(0)); 
}

This bug has been present already on 2014-11-21.

It's one-line fix, I'll try making a PR.

[Aatch]

Heh, that's kind of amusing.