有時候網路請求會異常，比如報錯：

NSURLConnection finished with error - code -1002

Response failed, error buffer: unsupported URL

處理方法:

iOS 8 要用utf8轉碼：

urlString = [urlString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

iOS 8 以後要用這個方法：

urlString = [urlString stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet characterSetWithCharactersInString:@"#%^{}\"[]|\\<> "].invertedSet];