[HttpClient] Don't ignore errors from curl_multi_exec()

Author: divinity76

Response/CurlResponse.php

@@ -274,7 +274,11 @@ private static function perform(ClientState $multi, array &$responses = null): v
         try {
             self::$performing = true;
             $active = 0;
-            while (\CURLM_CALL_MULTI_PERFORM === curl_multi_exec($multi->handle, $active));
+            while (\CURLM_CALL_MULTI_PERFORM === ($err = curl_multi_exec($multi->handle, $active)));
+
+            if (\CURLM_OK !== $err) {
+                throw new TransportException(curl_multi_strerror($err));
+            }
 
             while ($info = curl_multi_info_read($multi->handle)) {
                 $result = $info['result'];