Description:
------------
xmlrpc_encode and xmlrpc_encode_request works different if the properties $xmlrpc_type and $scalar are defined before assigning values to an object.

If the properties $xmlrpc_type and $scalar are defined, xmlrpc_encode* don't use the values for serialization.

Test script:
---------------
class Foo {
    
}

class Bar {
    
    public $xmlrpc_type;
    public $scalar;
    
}

$foo = new Foo();
$foo->xmlrpc_type = 'base64';
$foo->scalar = 'foobar';

$bar = new Bar();
$bar->xmlrpc_type = 'base64';
$bar->scalar = 'foobar';

$xml = xmlrpc_encode([
    'foo' => $foo,
    'bar' => $bar
]);
var_dump($xml);

Expected result:
----------------
<?xml version="1.0" encoding="utf-8"?>
<params>
<param>
 <value>
  <struct>
   <member>
    <name>foo</name>
    <value>
     <base64>Zm9vYmFy&#10;</base64>
    </value>
   </member>
   <member>
    <name>bar</name>
    <value>
     <base64>Zm9vYmFy&#10;</base64>
    </value>
   </member>
  </struct>
 </value>
</param>
</params>

Actual result:
--------------
<?xml version="1.0" encoding="utf-8"?>
<params>
<param>
 <value>
  <struct>
   <member>
    <name>foo</name>
    <value>
     <base64>Zm9vYmFy&#10;</base64>
    </value>
   </member>
   <member>
    <name>bar</name>
    <value>
     <struct>
      <member>
       <name>xmlrpc_type</name>
       <value>
        <string>base64</string>
       </value>
      </member>
      <member>
       <name>scalar</name>
       <value>
        <string>foobar</string>
       </value>
      </member>
     </struct>
    </value>
   </member>
  </struct>
 </value>
</param>
</params>