message: Fix panic in parsing of empty token code
diff: @@ -336,10 +336,9 @@ impl SpotifyOAuth {
  }
  /// Parse the response code in the given response url
  pub fn parse_response_code(&self, url: &mut str) -> Option<String> {
  - let tokens: Vec<&str> = url.split("?code=").collect();
  - let strings: Vec<&str> = tokens[1].split('&').collect();
  - let code = strings[0];
  - Some(code.to_owned())
  + url.split("?code=").nth(1)
  + .and_then(|strs| strs.split('&').next())
  + .map(|s| s.to_owned())
  }
  /// Gets the URL to use to authorize this app
  pub fn get_authorize_url(&self, state: Option<&str>, show_dialog: Option<bool>) -> String {
  