Fix building post data for object

PHP 8 error messages:
    TypeError: array_keys(): Argument #1 ($array) must be of type array, stdClass given
    TypeError: array_values(): Argument #1 ($array) must be of type array, stdClass given

PHP 7 error messages:
    TypeError: array_keys() expects parameter 1 to be array, object given
    TypeError: array_values() expects parameter 1 to be array, object given

src/Curl/Curl.php

@@ -208,7 +208,7 @@ class Curl
                 // php_url_encode()
                 // https://github.com/php/php-src/blob/master/ext/standard/http.c
                 return urlencode(strval($k)) . '=' . urlencode(strval($v));
-            }, array_keys($data), array_values($data)));
+            }, array_keys((array)$data), array_values((array)$data)));
         }
 
         return $data;

tests/PHPCurlClass/PHPCurlClassTest.php

@@ -81,6 +81,15 @@ class CurlTest extends \PHPUnit\Framework\TestCase
         ]));
     }
 
+    public function testBuildPostDataObject()
+    {
+        $data = new \stdClass();
+        $data->{'abc'} = 'foo';
+        $data->{'123'} = 'bar';
+        $curl = new Curl();
+        $curl->buildPostData($data);
+    }
+
     public function testUserAgent()
     {
         $php_version = preg_replace('/([\.\+\?\*\(\)\[\]\^\$\/])/', '\\\\\1', 'PHP/' . PHP_VERSION);