Description:
------------
SolrClient::getById/SolrClient::getByIds does not clear the request body before sending the request, causes invalid URL with tainted previously sent request

Test script:
---------------
require_once "bootstrap.inc";

$options = array
(
    'hostname' => SOLR_SERVER_HOSTNAME,
    'login'    => SOLR_SERVER_USERNAME,
    'password' => SOLR_SERVER_PASSWORD,
    'port'     => SOLR_SERVER_PORT,
    'path'     => SOLR_SERVER_PATH
);

$client = new SolrClient($options);

$doc = new SolrInputDocument();

$doc->addField('id', 'some_id');
$doc->addField('field1', 'val1');

$client->addDocument($doc);

$client->commit();

$response = $client->getById('some_id');

var_dump(isset($response->getArrayResponse()['doc'])).PHP_EOL;
var_dump($response->getResponse()->doc->id) . PHP_EOL;

Expected result:
----------------
bool(true)
string(7) "some_id"

Actual result:
--------------
Fatal Error: Uncaught SolrClientException: Solr HTTP Error 3: 'URL using bad/illegal format or missing URL'