Fix consumption errors in kafka against recent versions in librdkafka/phprdkafka

Recent versions may no longer return error message when reaching end of partition
(RD_KAFKA_RESP_ERR__PARTITION_EOF - due to change in `enable.partition.eof`).
This is especially true for librdkafka >=1.0.0.
see arnaud-lb/php-rdkafka#220 (comment)

Author: Paweł Niedzielski

pkg/rdkafka/RdKafkaConsumer.php

@@ -155,6 +155,10 @@ private function doReceive(int $timeout): ?RdKafkaMessage
     {
         $kafkaMessage = $this->consumer->consume($timeout);
 
+        if ($kafkaMessage === null) {
+            return null;
+        }
+
         switch ($kafkaMessage->err) {
             case RD_KAFKA_RESP_ERR__PARTITION_EOF:
             case RD_KAFKA_RESP_ERR__TIMED_OUT: