Fix crash when attribute NSLinkAttributeName is kind of NSString

[xspyhack]

TTTAttributedLabel does not handle NSLinkAttributeName attribute is kind of NSString, so it will use a NSString type value to init NSLinkCheckingResult by [NSTextCheckingResult linkCheckingResultWithRange:range URL:url]; // url is kind of NSString.

switch (result.resultType) {
    case NSTextCheckingTypeLink:
        if ([self.delegate respondsToSelector:@selector(attributedLabel:didSelectLinkWithURL:)]) {
            [self.delegate attributedLabel:self didSelectLinkWithURL:result.URL]; // the result.URL is kind of NSString, not NSURL
            return;
        }
        break;

#pragma mark - TTTAttributedLabelDelegate

- (void)attributedLabel:(TTTAttributedLabel *)label didSelectLinkWithURL:(NSURL *)url {
    // Crashed here when use url as `NSURL`.
}