If the email body is nil, don't try to split it again

This is one way to deal with #70 and #64.  Essentially the issue is that we're expecting a well formed body with a reply delimiter, but that may not be the case.  I moved the gsubs up top because those can happen early on, and then whenever we do an unsafe split I either return the first element or an empty string.

I actually would prefer something like this though:

```ruby
class String
  def safe_split(matcher)
    split_self = self.split(matcher)
    if split_self.empty?
      split_self = [""]
    end
    split_self
  end
end
```

I'm very hesitant to extend string though, so if you guys have a better solution LMK.